Influenza in Europe : season 2011-2012.
Date: 2015-03-16
Institutions: European Centre for Disease Prevention and Control
Subjects: Europe, disease prevention, epidemic, health policy, infectious disease, public health, research report, vaccination

SURVEILLANCE REPORT

Influenza in Europe
 Season 2011–2012

www.ecdc.europa.eu

ECDC SURVEILLANCE REPORT 

Influenza in Europe 

Season 2011–2012 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
This report of the European Centre for Disease Prevention and Control (ECDC) was coordinated by René Snacken, 
Contributing authors 
Eeva Broberg, Julien Beauté, Flaviu Plata, Phillip Zucs and Angus Nicoll. 

Acknowledgements: The authors gratefully acknowledge the members of the European Influenza Surveillance 
Network, the WHO Influenza Collaborating Centre, the CNRL, Euromomo and I-MOVE for their support in the 
production of this report: 

Viorel  Alexandrescu, Alessandro Annunziato, Ivan Bakoss, Christopher  Barbara, Antonino  Bella, Nataša Berginc, 
Oliver Blatchford, Isabelle  Bonmarin, Karoline Bragstad, Caroline Sarah Brown, Susan Brownlie, Lidia  Brydak, Mia 
Brytting, Silke Buda, Paul Cabrey, William F Carman, Anna Sara Carnahan, Inmaculada Casas Flecha, Eva 
Chmelanova, Glenn Codere, Jean Marie Cohen, Suzie Coughlan, Helena Dahl, Rodney Stuart Daniels, Marit de 
Lange, Irene Demuth, Frederika Dijkstra, Eudoxia Diza, Isabella Donatelli, Gé Donker, Margaret Duffy, Susanne 
Duwe, Anne Eastaway, Avraam Elia, Joanna Ellis, Vincent Enouf, Joy Field, Nichola Goddard, Zahra Graziella, Helen 
Green, Algirdas Griskevicius, Rory Gunson, Siri Helene Hauge, Ariane Halm, Martina Havlickova, Alan J. Hay, 
Kenneth Hebing, Anneleen Hombrouck, Kate Howell, Helena Hudecova, Olav Hungnes, Niina Ikonen, Viera 
Janculova, Istvan Jankovics, Helena Jirincova, Fiona Johnston, Katalin Kaszas, Cathriona Kearns, Farhad  Khan, 
Esther Kissling, Neli Korsun, Athanassios Kossivakis, Veronika Kostalova, Gérard Krause, Lisbet Krause Knudsen, 
Natalja Kuznetsova, Peter Lachner, Angie Lackenby, Jarmila  Lancova, Amparo Larrauri Cámara, Daniel Lévy-Bruhl, 
Bruno Lina, Vilnele Lipnickiene, Hazel Littler, John Love, Arthur Löve, Emilia Lupulescu, Jackie Maistre Melillo, Anne 
Mazick, John McCauley, Elizabeth McCruden, Jim Mcmenamin, Adriana  Mecochova, Adam Meijer, Andreas Mentis, 
Maria  Meropi Charalambous, Ján Mikas, Kåre Mølbak, Catherine Moore, Joanne Moran, Raquel Moreira Guiomar, 
Alain Moren, Anne Mosnier, Heatlher Murdoch, Monika Musilová, Raina Nikiforova, Baltazar Nunes, Chinelo Obi, 
Christophe Olinger, Matthias Opp, Raul Ortiz De Lejarazu Leonardo, Egle Pauzaite, Richard Pebody, Despo Pieridou 
Bagatzouni, Lesja  Pokras, Rodica Manuela Popescu, Odette Popovici, Theresia Popow–Kraupp, Francisco Pozo 
Sanchez, Katarina  Prosenc, Tomas Pumarola, Helena Rebelo De Andrade, Monika Redlberger-Fritz, Arlene 
Reynolds, Guus Rimmelzwaan, Caterina Rizzo, Monika Rozsa, Olga Sadikova, Gerard Scheiden, Brunhilde 
Schweiger, Praveen Sebastianpillai, Elsin  Shakir, Louise Shaw, Brian Smyth, Bianca Snijders, Edita Staronová, 
Isabelle Thomas, Daniel Thomas, Catherine Thompson, Marta Valenciano, Martine Valette, Viviane Van Casteren, 
Wim Van der Hoek, Sylvie van der Werf, Tomas Vega, Karen Voy, Allison Waters, John Watson, Asa Wiman, 
Agnieszka Wozniak-Kosek, Françoise Wuillaume, Maria Zambon, Natalija Zamjatina, Alexandra Zampachova and 
Thedi Ziegler. 

Errata  
The following corrections were made on 24 October 2012.  
Page 12: the original early season estimate of 43 % vaccine effectiveness was changed to between 43% and 55%.  
Page 13: a reference was added in relation to the above change. 

Suggested citation: European Centre for Disease Prevention and Control. Influenza in Europe – Season 2011–2012. 
Stockholm: ECDC; 2012. 

Stockholm, October 2012 

ISBN 978-92-9193-380-8 

doi 10.2900/61975 

© European Centre for Disease Prevention and Control, 2012 

Reproduction is authorised, provided the source is acknowledged 

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Influenza surveillance in Europe 2011–2012 

Contents 

Abbreviations ............................................................................................................................................... iv 
Executive summary ........................................................................................................................................ 1 
1. Background ............................................................................................................................................... 2 
2. Objectives ................................................................................................................................................. 3 
Table 1.Objectives of human influenza surveillance in Europe ............................................................................ 3 
3. Methods .................................................................................................................................................... 4 
3.1. Period and countries under surveillance ................................................................................................ 4 
3.2. Primary care surveillance .................................................................................................................... 4 
3.3. Hospital surveillance ........................................................................................................................... 5 
4. Results ...................................................................................................................................................... 6 
4.1. Primary care ...................................................................................................................................... 6 
4.2. Hospitalisations due to influenza ........................................................................................................ 10 
5. Discussion ............................................................................................................................................... 12 
6. Conclusions ............................................................................................................................................. 12 
7. Bibliography ............................................................................................................................................ 13 
Annex 1. Clinical influenza surveillance numerator and denominator by country ................................................. 14 

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Abbreviations 

ARI 
CNRL 
ECDC 
EISN 
EISS 
EU  
EEA 
EMA 
Euromomo  
GP 
GISRS 
ILI 
ITU 
MEM 
RSV 
SARI 
TESSy 
VENICE   
WHA 
WHO 

Acute respiratory infection 
Community Network of Reference Laboratories for Human Influenza in Europe 
European Centre for Disease Prevention and Control 
European Influenza Surveillance Network 
European Influenza Surveillance Scheme 
European union 
European economic area  
European Medicines Agency 
European monitoring of excess mortality for public health action 
General practitioner 
Global Influenza Surveillance and Response System 
Influenza-like illness 
Intensive treatment unit 
Moving epidemic method 
Respiratory syncytial virus 
Severe acute respiratory infection 
The European Surveillance System 
Vaccine European New Integrated Collaboration Effort 
World Health Assembly 
World Health Organization 

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Influenza surveillance in Europe 2011–2012 

Executive summary 

The 2011–12 influenza season started later than usual and did not exhibit any clear pattern of geographic 
progression. Compared to the previous seasons, the intensity was mild, except in four countries where the ILI/ARI 
rates were slightly higher than average. Among influenza A viruses detected in sentinel patients and subtyped, 
A(H3N2) viruses vastly outnumbered A(H1N1)pdm09 viruses (98.5% vs. 1.5%). The proportion of influenza type B 
viruses increased after week 5/2012 and two different lineages circulated in similar proportions until the end of the 
epidemic, although at low numbers compared with the A(H3N2) viruses.  

In severe influenza cases that were hospitalised, the most frequently isolated virus was A(H3N2) and larger 
proportions of cases were observed in the youngest and oldest age groups. Mortality from all causes increased in 
persons ≥ 65 years and peaked in week 7/2012, but other studies are needed to estimate the influenza-related 
mortality, especially as a period of cold weather occurred concomitantly in most countries reporting to the 
European mortality monitoring project, Euromomo. No resistance to neuraminidase inhibitors was observed. 
Antigenic and genetic characterisations of circulating strains showed an imperfect match with the A(H3N2) 
component of the current influenza vaccine. Observational studies later confirmed a reduced vaccine effectiveness. 
These findings support the decision of the World Health Organization (WHO) to recommend a change in the 
seasonal influenza vaccine composition for the 2012–2013 season.  

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1. Background 

The coordination of influenza surveillance in Europe started in 1987 in successive schemes: Eurosentinel, ENS Care 
and the European Influenza Surveillance Scheme (EISS). Later, the project was funded by the European 
Commission and influenza surveillance was extended to all EU countries1 . In 2003, a Community Network of 
Reference Laboratories for Human Influenza in Europe (CNRL) was established, with participation of the United 
Kingdom-based World Health Organization (WHO) Collaborating Centre, to standardise virological methods across 
Europe and regularly assess and improve the quality of laboratory performance (Meijer et al. 2005). Since 2008, 
the coordination of the influenza surveillance network, now called the European Influenza Surveillance Network 
(EISN), has been transferred to the European Centre for Disease Prevention and Control (ECDC) by agreement and 
under legislation. National data are reported to The European Surveillance System (TESSy) of ECDC. All data are 
also supplied to the WHO Global Influenza Surveillance and Response System (GISRS)2 through working closely 
with the WHO Regional Office for Europe and the WHO Collaborating Centre based in Europe.  

As recommended by the World Health Assembly (WHA) and done in the 2009 pandemic, ECDC published an 
annual risk assessment 3 as early as possible in the 2011/12 season (9 March), providing preliminary data analyses 
from first affected countries to inform the whole of Europe (Nicoll A, 2011, WHO report, 2011). For this purpose, 
data were collected by questionnaire, pooled with information from epidemic intelligence and reviewed by external 
experts. As in the risk assessment performed in 2010/114, the objectives were to: give an early description of the 
situation in first affected countries; to estimate the possible pressure on primary and secondary healthcare services 
(impact); to obtain information from other sources or networks such as Euromomo (mortality, Mazick A. et al. 
2012), WHO, Vaccine European New Integrated Collaboration Effort (VENICE) (vaccine coverage and policies, 
Mereckiene J et al. 2010), I-MOVE (Influenza Monitoring Vaccine Effectiveness in Europe, Kissling E. et al. 2009) 
and the European Medicines Agency (EMA) (vaccine safety); and to address uncertainties, where possible, and the 
public health actions indicated.  

1 Decision 2000/96/EC. Available at: http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2003:185:0055:0058:en:PDF 
2 http://www.who.int/influenza/gisrs_laboratory/en/ 
3 Available at: http://ecdc.europa.eu/en/publications/Publications/120312-TER-Seasonal-influenza-risk-assessment.pdf 
4 Available at: http://ecdc.europa.eu/en/publications/Publications/110125_RA_Seasonal_Influenza_EU-EEA_2010-2011.pdf 

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Influenza surveillance in Europe 2011–2012 

2. Objectives 

The main objectives of influenza surveillance are to describe the epidemiology and virological characteristics of 
influenza in primary healthcare and hospital settings. Weekly results are available on the ECDC website and there 
is an overall aim of contributing to the Global Influenza Surveillance and Response System of WHO. Specific 
objectives are: 

• 
• 

• 

• 
• 

• 

• 

to estimate the overall intensity of influenza activity, the geographic spread, impact and trends; 
to also estimate the influenza activity with sentinel virological data, i.e. the percentage of specimens 
positive for influenza;  
to identify the influenza types and subtypes in circulation and the dominant type from sentinel and non-
sentinel sites; 
to check whether circulating strains are susceptible to antiviral treatment; 
to analyse variations in antigenic and genetic characterisations, to assess the match with vaccine strains 
and to estimate vaccine effectiveness; 
to assess the role of respiratory syncytial virus (RSV) circulation on the burden of influenza-like illness 
(ILI)/Acute respiratory infection (ARI), especially in young infants; 
to describe epidemiological characteristics of severe (hospitalised) influenza cases and deaths, and to 
determine influenza (sub)types responsible for them; 

During and after the 2009 influenza pandemic and evaluations of the response, ECDC placed particular emphasis 
on a more risk-based approach. Consequently, the surveillance outputs are linked to a series of specific public 
health and clinical objectives with related actions (Table 1). 

Table 1.Objectives of human influenza surveillance in Europe  

Objectives: Determining  
Circulating influenza viruses 

Duration, shape, number and tempo of the waves of infection 
across Europe 
Antigenic and genetic characterisations  

Susceptibility/resistance to antiviral drugs  

Age and clinical groups most infected and affected 

Susceptibility in the population-age groups with most 
transmission (seroepidemiology) 
Clinical presentation of severe disease and impact, complicating 
other infections and underlying disease (including 
cerebrovascular and cardiovascular) 
Unusual features of clinical presentations  

Complicating conditions (superinfections etc.) 

Pathogenicity (case/infection fatality rates) 

Excess premature mortality by age group  

‘Impact and severity’ of an influenza epidemic (or pandemic) (a 
complex variable best seen as a matrix) 

Effectiveness and safety of interventions and counter-measures 
including influenza vaccines and antiviral pharmaceuticals-
detecting treatment and preventive failure, monitoring and 
evaluating vaccination programmes 

Public health purpose 
Supplying information on start and circulation of influenza in and between 
countries 
Informing countries yet to be affected, especially about the intensity and impact 
so that preparations can be made 
Supplying information and isolates to the Global Influenza Surveillance and 
Response System (GISRS) of WHO to collectively review and update the annual 
seasonal vaccine. 
Early detection of new variants (untypable and unsubtypable strains)-potential 
emergence of pandemic strain, animal-to-human transmissions 
Detecting the emergence of resistant viruses indicating a need to amend 
recommendations for the use of antiviral drugs 
Reviewing and optimising recommendations on the groups to be targeted for 
immunisation and antivirals (risk and other target groups) 
idem 

Informing testing and case-detection policies 
Alerting clinicians to new clinical presentations.  

Informing testing and case-detection policies 
Alerting clinicians to new clinical presentations 
Informing testing and case-detection policies 
Alerting clinicians to new clinical presentations and complications 
Estimating impact and burden of disease and helping inform policy on 
interventions, including vaccination  
Estimating burden of disease and helping inform policy on interventions, 
including vaccination 
Information about the possible pressure on health care services including 
primary care, emergency rooms, secondary care, intensive treatment units (ITU) 
and so alerting clinicians and managers on whether to implement contingency 
plans 
Informing decisions on vaccines and antivirals for regulatory agencies, clinicians, 
the public, researchers and industry.  

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3. Methods 

3.1. Period and countries under surveillance 

The influenza surveillance season in Europe lasts from week 40 (beginning of October) of any given year to week 
20 (mid-May) of the following year. Between seasons, more limited information is gathered on the virological 
characteristics of circulating viruses, quantitative clinical data and severe acute respiratory infections. ECDC also 
maintains a year-round epidemic intelligence function to detect unusual events including those possibly related to 
influenza transmission. This report describes data and analyses from week 40/2011 to week 20/2012. Data were 
received from all EU Member States, Iceland and Norway, but not all participating countries contributed to each 
component of the surveillance system every week.  

3.2. Primary care surveillance 

3.2.1. Clinical surveillance 

Influenza-like illness /acute respiratory infection surveillance is carried out by nationally organised sentinel 
networks of physicians, mostly general practitioners (GPs), covering at least 1% and up to 5% of the population in 
their countries (Lobet MP et al., 1987).  
Recommended clinical case definitions of both ILI and ARI are the following EU definitions 5: 

For ILI: 

• 
• 

• 

sudden onset of symptoms; 
AND at least one of the following four systemic symptoms: fever or feverishness, malaise, headache, 
myalgia; 
AND at least one of the following three respiratory symptoms: cough, sore throat, shortness of breath. 

For ARI: 

• 
• 

• 

sudden onset of symptoms; 
AND at least one of the following four respiratory symptoms: cough, sore throat, shortness of breath, 
coryza; 
AND a clinician’s judgement that the illness is due to an infection. 

Both indicators are adequate in estimating influenza activity (Paget et al. 2007). As a denominator, most countries 
use population covered by GPs which allows the calculation of rates per 100 000 inhabitants, while some use the 
total number of consultations by 100 GPs. 

Sentinel physicians report the weekly number of patients seen with ILI, ARI or both (broken down by age groups), 
and the denominator, to a nominated national focal point who then reports the data to ECDC. Numerators and 
denominators by country, and definitions of epidemiological indicators are available in annex 1. 

During the 2011–12 season, a pilot model, the moving epidemic method (MEM), was used by eight countries to 
define a baseline of influenza activity and to calculate a pre- and post-epidemic threshold. These thresholds were 
calculated with data from previous years (Vega et al. 2012). One additional country used its own baseline and 
thresholds. This method generates: 

• 
• 

• 

• 

an average curve based on historical data (five years or more); 
a pre-epidemic threshold (horizontal line at the beginning of the season): when exceeded by the ILI/ARI 
curve, the week is considered the start of the epidemic period with 95% confidence (virological confirmation 
is needed); 
a post-epidemic threshold (horizontal line at the end of the season): when crossed by the decreasing curve 
of the current season, the epidemic can be declared over with 95% confidence (here again, no or few 
isolates should be detected); the number of weeks between the end of the pre-epidemic and the beginning 
of the post-epidemic period is the duration of the epidemic; 
a 90% confidence interval: when the current curve is peaking above this threshold, it means that the 
current epidemic is above 90% of historical peak values. 

The epidemic thresholds are displayed on the ECDC website for countries that have agreed to it (link here, select 
season table by week, select specific epidemiological graph).  

5 Available at: http://ecdc.europa.eu/en/activities/surveillance/EISN/surveillance/Pages/influenza_case_definitions.aspx 

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Influenza surveillance in Europe 2011–2012 

3.2.2. Virological surveillance 

The sentinel physicians take nasal and/or pharyngeal swabs from a subset of their ILI/ARI patients according to 
nationally defined sampling strategies. The specimens are sent to the national CNRL laboratory for influenza virus 
detection, typing and subtyping. Further analyses, for instance antigenic and genetic characterisation and antiviral 
susceptibility testing, are performed by some national reference centres or CNRL consortium laboratories (WHO 
Collaborating Centre for Reference and Research on Influenza at the Medical Research Centre in London). 
Influenza viruses detected in samples that were not collected in sentinel healthcare settings are also reported. 
Some laboratories also test these specimens for the presence of RSV and other respiratory viruses (the latter are 
not reported to TESSy). Laboratory results, including those obtained for non-sentinel specimens, are reported to 
ECDC by nominated national focal points every week. 

3.3. Hospital surveillance 

Seven countries reported hospital surveillance data in 2011/12. Four countries (France, Ireland, Spain and the 
United Kingdom) reported only hospitalised cases due to confirmed influenza infection while three countries 
(Belgium, Romania and Slovakia) reported severe acute respiratory infection (SARI) cases caused by influenza or 
any other pathogen (Beauté J et al. 2012). 

A clinical SARI case was defined as: 

• 
• 
• 
• 

sudden onset of fever over 38°C, and 
cough or sore throat in the absence of any other diagnosis, and 
shortness of breath or difficulty breathing, and 
requiring hospital admission. 

Data were reported to ECDC on a weekly basis. 

Collected variables were demographic data (age, gender), clinical data (underlying conditions, clinical presentation, 
oxygen support, complications, fatal outcome), virological data (influenza type, subtype, other respiratory 
pathogen), level of hospital care (intensive treatment unit, regular care), antiviral treatment (including prophylaxis) 
and vaccination status. Cases were reported by the so-called ‘date used for statistics’ which is a date applied by the 
reporting country for the publication of data at national level. This date could be the date of onset, notification, 
hospitalisation or any other date. 

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4. Results 

4.1. Primary care 

4.1.1. Clinical surveillance 

The 2011–12 influenza season in Europe, the second season after the 2009 pandemic, started late, in week 3/2012, 
when five countries reported medium intensity of influenza activity (Bulgaria, Iceland, Italy, Malta and Spain) and 
nine countries reported local or regional geographic spread. There was no clear geographic progression. ILI/ARI 
rates peaked during weeks eight and nine (range: 5–11) when 18 countries reported medium intensity. In week 
eight, 19 countries reported regional or widespread activity (see figure 1).The intensity of ILI/ARI primary care 
consultations as compared with the 2010/11 season was notably mixed across countries. In Iceland, Malta, 
Portugal and Sweden, it was comparable or slightly higher. In the Czech Republic, Denmark, Lithuania, Romania, 
Slovakia and the United Kingdom, intensity was considerably lower than in the previous season. In almost all 
reporting countries, the most affected age group was 0–4 years. 

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Influenza surveillance in Europe 2011–2012 

Figure 1. Geographic spread for week 8/2012 

4.1.2. Virological surveillance 

In the 2011–2012 surveillance period, 9 472 respiratory specimens from sentinel patients tested positive for 
influenza: 8 462 (89.3%) for influenza A viruses and 1 011 (10.7%) for influenza B viruses (table 2). The latter 
became dominant at the end of the epidemic even though the absolute number of detected viruses was decreasing 
(figure 2). 

Of 7 799 sentinel influenza A viruses subtyped, 7 682 (98.5%) were A(H3) viruses and 117 (1.5%) were 
A(H1)pdm09 viruses. No A(H1N1) virus circulating before 2009 was detected. The lineage of 187 influenza B 
viruses was determined: 113 (60.4%) were B-Victoria and 74 (39.6%) were B-Yamagata lineage (table 2). 

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Table 2. Number of influenza virus detections by type, subtype and lineage from week 40/2011 to 
week 20/2012 in 29 EU/EEA countries. 

Virus type/subtype 

Season sentinel 

Influenza A 

A(H1)pdm09 

A(H3) 

A(sub-type unknown) 

Influenza B 

B(Vic) lineage 

B(Yam) lineage 

Unknown lineage 

Total influenza 

8462 

117 

7682 

663 

1011 

113 

74 

824 

9473 

Figure 2. Number of sentinel specimens testing positive for influenza A and B from week 40/2011 to 
week 20/2012 in 29 EU/EEA countries. 

The weekly percentage of sentinel specimens positive for influenza peaked in week 8/2012 (figure 3).  

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Figure 3. Number of sentinel specimens and proportion of specimens positive for influenza virus from 
week 40/2011 to week 20/2012 in 29 EU/EEA countries. 

Antigenic and genetic characterisation of circulating viruses  

From week 40/2011 to week 20/2012, 1 796 antigenic characterisations of viruses were reported, of which 1 335 
(74.3%) were A/Perth/16/2009 (H3N2)-like. Sixty-eight viruses were reported without category: 40 A(H3), 19 
B(Yamagata-lineage) and 9 B(Victoria-lineage) viruses, reflecting changes in the reference viruses towards the end 
of the season. 

From week 40/2011 to week 20/2012, 1 385 genetic characterisations of viruses were reported, 1 177 (85.0%) of 
which were A(H3) viruses. Of the latter, 684 (58.1%) fell within the A/Victoria/208/2009 clade, genetic group 3 
represented by A/Stockholm/18/2011. Viruses falling within this genetic group are antigenically diverse, causing an 
imperfect match with the current vaccine virus, A/Perth/16/2009.  

The antigenic distance between wild and vaccine virus was also suggested by results from the CNRL showing that 
recently circulating A(H3N2) viruses yielded low titres with post-infection ferret antisera raised against 
A/Perth/16/2009 (CNRL, 2012). 

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Antiviral resistance 

From week 40/2011 to week 20/2012, influenza viruses were tested for antiviral susceptibility by ten countries. 
None of the A(H1)pdm09, A(H3) and B viruses tested against neuraminidase inhibitors showed resistance or 
reduced susceptibility. All A(H1)pdm09 and A(H3) viruses assessed for M2 blocker susceptibility were resistant 
(table 3). 

Table 3. Antiviral resistance by influenza virus type and subtype in ten EU/EEA countries, weeks 
40/2011 to 20/2012 

Virus type 
and subtype 

Resistance to neuraminidase inhibitors 

Resistance to M2 inhibitors 

Oseltamivir 

Zanamivir 

Isolates 
tested 

Resistant  % 

Isolates 
tested 

Resistant  % 

Isolates 
tested 

Resistant  % 

A(H3) 

778 

A(H1)pdm09 54 

B 

68 

0 

0 

0 

0 

0 

0 

765 

54 

63 

0 

0 

0 

0 

0 

0 

179 

179 

11 

NA 

11 

NA 

100 

100 

NA 

NA = not applicable, as M2 inhibitors do not act against influenza B viruses. 

Data are from single location (e.g. H275Y only) or multiple location mutation analysis (full sequencing) and/or phenotypic 
characterisation (IC50 determination; a cut-off of 100nM oseltamivir/zanamivir/M2 blockers for subtypes H1and H3 and 200 nM 
oseltamivir/zanamivir for B viruses has been applied for inclusion). Therefore, data should be interpreted in this context. 

Respiratory syncytial virus  

Compared to the previous year, the time series of weekly detections of RSV in 15 EU countries was similar, but 
peaking one week earlier figure 4). 

Figure 4. Sentinel and non-sentinel respiratory syncytial virus (RSV) detections during seasons 2010-
2011 and 2011-2012 in 15 EU countries 

4.2. Hospitalisations due to influenza 

From week 40/2011 to week 20/2012, four countries reported 1 164 hospitalised laboratory-confirmed influenza 
cases (19 cases reported by France were excluded because the laboratory information was missing) while three 
countries reported 646 SARI cases, of which 152 (23.5%) had laboratory-confirmed influenza infections. The 
proportion of SARI cases aged below five years was significantly higher in non-confirmed cases (50 % vs 30 %; p 
< 0.01). The number of SARI cases reported peaked during week eight of 2012 (figure 5) shortly after the peak of 
hospitalised laboratory-confirmed influenza cases in week seven (figure 6). 

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Figure 5. Sari cases and proportion due to influenza infection by week of reporting in Belgium, 
Romania and Slovakia, weeks 40/2011–20/2012 

Figure 6. Number of hospitalised laboratory-confirmed influenza cases in seven EU countries by week 
of reporting, weeks 40/2011–20/2012. 

Overall, an influenza virus infection was laboratory-confirmed in 1 316 cases, of which 1 269 (96.4%) were type A 
and 47 (3.6%) were type B. Of the 1 269 influenza A viruses, 774 (61.0%) were A(H3), 47 (3.7%) were 
A(H1)pdm2009 and 448 (35.3%) were not subtyped. The male to female ratio was 1.2:1. The distribution of cases 
by age group was driven by the most frequently isolated virus subtype A(H3) and showed the largest proportion of 
cases in the youngest and oldest age groups (Figure 7). Of the 845 hospitalised influenza laboratory-confirmed 
cases with known outcome, 98 (11.6%) died. The median age of the 98 fatal cases was 75 years.  

Of 560 hospitalised influenza laboratory-confirmed cases with information on underlying conditions, 452 
(80.7%) had at least one recognised risk factor for severe disease, most commonly chronic respiratory disease 
(131), cardiac disease (90) and diabetes (82).Of the 723 hospitalised influenza laboratory-confirmed cases with 
known vaccination status, 489 (67.6%) were not vaccinated. 

Figure 7. Number of hospitalised laboratory-confirmed influenza cases in Belgium, France, Ireland 
Romania, Slovakia and Spain, by type, subtype and by age group, weeks 40/2011 to 20/2012. 

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5. Discussion 

Results from routine surveillance during the 2010–2012 season were in accordance with the results of the 
abovementioned risk assessment performed in early 2012, in addition to other observational studies. 

This late and mild influenza season did not exhibit a west-east progression as observed during previous seasons 
(1999-2007) (Paget J. et al., 2007). 

The antigenic diversity in characterisations of A(H3N2) viruses and low titres observed with post-infection ferret 
antisera raised against A/Perth/16/2009 caused an imperfect match with the vaccine strain. This is consistent with 
the results of studies showing low vaccine effectiveness (Kissling E. et al., 2012, Bonmarin I. et al., 2012). Early 
season estimates of vaccine effectiveness varied from 43% and 55%, considerably lower than in 2010–2011 and 
2009–2010 (Jiménez-Jorge S. et al., 2012, Kissling E. et al. 2012). In addition, it is known that the percentage 
continued to decline as the season progressed (Kissling E. et al., 2012. Jiménez-Jorge S. et al., 2012). This is 
consistent with outbreaks in well vaccinated populations (Castilla J et al., 2012) and the WHO’s decision to 
recommend a change to an A/Victoria/361/2011-like (H3N2) virus in the trivalent influenza vaccines for the 
northern hemisphere 2012–13 influenza season (WER 2012). 

The dominance of A(H3N2) was predicted by annual serological studies performed by Norway and Poland. In 
Norway, the prevalence of protective antibodies to A(H3N2) in people aged 25–49 was very low (4 %) and 
therefore they were supposed to be more prone to infection by this subtype. However, the prevalence of 
antibodies against A(H3N2) in school-aged children was high (31 %). In the Norwegian risk assessment, it was 
stated that the season would be dominated by A(H3N2), which was the case (Norwegian institute of Public Health 
report, 2012). In Poland, protective antibody titres against A(H3N2) influenza viruses were highest in the age 
group 15 to 25 (40.5%) and 8- to 14-year olds (33.8%). (L.Brydak, personal communication).These results 
suggest that there are country-specific variations in the presence of pre-existing antibodies and different age 
groups might be affected in different countries.  

With the dominance of A(H3N2), a shift to older ages, especially in cases with underlying conditions,  was 
observed in severe influenza cases reported by four EU countries.  

In the risk assessment performed during the first months of 2012, an excess mortality from all causes had already 
been observed in February in three countries — Belgium, the Netherlands and Portugal — in persons ≥ 65 years. 
As these countries experienced very low temperatures when the influenza activity was increasing, differentiating 
the cause of premature deaths is difficult (Nicoll A et al., 2012). During the 2011–12 season, a moderate excess 
mortality was observed in 12 EU countries between week five and week 11/2012, with a peak in week seven/2012 
in persons ages ≥ 65 years, possibly related to influenza with added effects of a cold snap (Mazick A. et al. 2012). 

6. Conclusions 

The influenza season 2011/12 started late and there was no particular pattern in its geographical progression  

The intensity of ILI/ARI activity was mild or unusually low in the majority of countries, although in four countries it 
was slightly higher than the previous season. Infants aged 0–4 years were the most affected outpatients and were 
the second largest age group after the elderly in hospitalised influenza cases reported by four EU countries. With 
the return of A(H3N2) virus, a shift to older ages in severe influenza cases was observed. An enhanced reporting of 
hospitalised influenza cases and influenza-related deaths at EU level would help to better estimate the severity of 
the disease.  

Even if A(H1N1)pdm09 viruses continued to circulate, they were largely exceeded by A(H3N2) and by B viruses, 
with the latter being especially important late in the season. The dominance of A(H3N2) viruses was hardly 
surprising, given the fact that there had not been an A(H3N2)-dominated season since 2006/07 which is in 
accordance with sero-epidemiological studies showing a low prevalence of protective antibodies, especially in 
young age-groups. Additional data on sero-epidemiology would be useful even if they are difficult to interpret 
because of the lack of standardisation of serological tests.  

Genetic characterisations of A(H3N2) viruses have shown important antigenic diversity resulting in an imperfect 
match with the vaccine strain. This was also reflected in the relatively low vaccine effectiveness observed and led 
to the WHO decision to recommend changing composition of the next influenza vaccine. 

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Influenza surveillance in Europe 2011–2012 

7. Bibliography 

Beauté J, Broberg E, Plata F, Bonmarin I, O’Donnell J, Delgado C, et al., ‘Overrepresentation of influenza A(H1N1)pdm09 virus 
among severe influenza cases in the 2011/12 season in four European countries’, Eurosurveill 2012; 17(9). Available online: 
http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=20105. 

Bonmarin I, Belchior E, Le Strat Y, Lévy-Bruhl D. First estimates of influenza vaccine effectiveness among severe influenza cases, 
France, 2011/12. Eurosurveill 2012;17(18):pii=20163. Available online: 
http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=20163 

Castilla J, Cía F, Zubicoa J, Reina G, Martínez-Artola V, Ezpeleta C. Influenza outbreaks in nursing homes with high vaccination 
coverage in Navarre, Spain, 2011/12. Eurosurveill 2012;17(14):pii=20141. Available online: 
http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=20141 

CNRL report on Influenza virus characterisation, ECDC June 2012. Available online: 
http://www.ecdc.europa.eu/en/publications/Publications/Influenza-visus-characterisation-June-2012.pdf 

S Jiménez-Jorge et al. Early estimates of the effectiveness of the 2011/12 influenza vaccine in the population targeted for 
vaccination in Spain, 25 December 2011 to 19 February 2012. Eurosurveill 2012;17 (12): pii=20129. Available online: 
http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=20129 

Kissling E, Valenciano M, Falcão JM, Larrauri A, Widgren K, Pitigoi D et al. “I-MOVE” towards monitoring seasonal and pandemic 
influenza vaccine effectiveness: lessons learnt from a pilot multi-centric case-control study in Europe, 2008–9. Eurosurveill 2009; 
Vol 14 (44): 1–8. Available on line: http://www.eurosurveillance.org/images/dynamic/EE/V14N44/art19388.pdf 

Kissling, E, Valenciano M, I-MOVE case–control studies team . ‘Early estimates of seasonal influenza vaccine effectiveness in 
Europe among target groups for vaccination: results from the I-MOVE multicentre case-control study, 2011/12’, Eurosurveill 2012; 
17(15), 1–7. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=20146 

Lobet, MP, Stroobant A, Mertens R, Van Casteren V, Walckiers D, Masuy-Stroobant G et al., Tool for validation of the network of 
sentinel general practitioners in the Belgian health care system. Intern J Epidemiol 16(4), 1987, pp. 612–8. 

Mazick A, Gergonne B, Nielsen J, Wuillaume F, Virtanen MJ, Fouillet A, et al. Excess mortality among the elderly in 12 European 
countries, February and March 2012. Eurosurveill. 2012;17(14):pii=20138. Available online: 
http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=20138 

Meijer A, Valette M, Manuguerra JC, Pérez-Breña P, Paget J, Brown C. et al., Implementation of the community network of 
reference laboratories for human influenza in Europe. J Clin Virol 34(2), 2005, pp. 87–96. 

Mereckiene J, Cotter S, D'Ancona F, Giambi C, Nicoll A, Lévy-Bruhl D et al, on behalf of the VENICE project gatekeepers group. 
Differences in national influenza vaccination policies across the European Union, Norway and Iceland 2008–2009. Eurosurveill. 
2010;15(44):pii=19700. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19700 

Nicoll A. Planning for uncertainty: a European approach to informing responses to the severity of influenza epidemics and 
pandemics Bulletin of the World Health Organization 2011;89:542–544. doi: 10.2471/BLT.11.089508. Available on line: 
http://www.who.int/bulletin/volumes/89/7/11-089508/en/index.html 

Nicoll A, Ciancio BC, Lopez Chavarrias V, Mølbak K, Pebody R, Pedzinski B et al. Influenza-related deaths - available methods for 
estimating numbers and detecting patterns for seasonal and pandemic influenza in Europe . Euro Surveill. 2012;17(18):pii=20162 
Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=20162 

Norwegian Institute of Public Health Report, 2012. Folkehelse instituttet. Rapport om scenarioer for influensaepidemi i 2012, 23. 
January 2012. Available online: http://www.fhi.no/dav/042f3a2a9d.pdf 

Paget J, Marquet R, Meijer A, van der Velden K et al., Influenza activity in Europe during eight seasons (1999–2007): an 
evaluation of the indicators used to measure activity and an assessment of the timing, length and course of peak activity (spread) 
across Europe.  BMC Infect Dis 7, 2007, p. 41 (doi:10.1186/1471-2334-7-141). 

Vega T, Lozano JE, Meerhoff T, Snacken R, Mott J, Ortiz de Lejarazu R et al., Influenza surveillance in Europe: establishing 
epidemic thresholds by the moving epidemic method. Influenza and Other Respiratory Viruses, August 2012.DOI: 
10.1111/j.1750–2659.2012.00422.x 

Weekly Epidemiological Record 2012; 10 (87): 85–91. Available at: http://www.who.int/wer/2012/wer8710.pdf 

WHO Report of the Review Committee on the Functioning of the International Health Regulations (2005) and on Pandemic 
Influenza A (H1N1) 2009 (Fineberg Report) Final submitted to the World Health Assembly 2011. Available online: 
http://apps.who.int/gb/ebwha/pdf_files/WHA64/A64_10-en.pdf 

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SURVEILLANCE REPORT 

Annex 1. Clinical influenza surveillance 
numerator and denominator by country 

Country 

Austria 

Belgium 

Bulgaria 

Cyprus 

Czech Republic 

Denmark 

Estonia 

Finland 

France 

Germany 

Greece 

Hungary 

Iceland 

Ireland 

Italy 

Latvia 

Lithuania 

Luxembourg 

Malta 

Netherlands 

Norway 

Poland 

Portugal 

Romania 

Slovakia 

Slovenia 

Spain 

Sweden 

United Kingdom — England 

United Kingdom — Northern Ireland 

United Kingdom — Scotland 

United Kingdom — Wales 

Numerator 

Denominator 

ARI, ILI 

ILI, ARI 

ARI 

ILI 

ILI, ARI 

ILI, ARI 

ILI, ARI 

– 

ARI 

ARI 

ILI 

ILI 

ILI 

ILI 

ILI 

ILI, ARI 

ILI, ARI 

ILI, ARI 

ILI 

ILI 

ILI 

ILI 

ILI 

ILI, ARI 

ILI, ARI 

ILI, ARI 

ILI 

ILI 

ILI, ARI 

ILI, ARI 

ILI, ARI 

ILI 

Population 

Population 

Population 

Encounters 

Population 

Population 

Population 

– 

Population 

Population 

Population 

Population 

Population 

Population 

Population 

Population 

Population 

Encounters 

Encounters 

Population 

Population 

Population 

Population 

Population 

Population 

Population 

Population 

Population 

Population 

Population 

Population 

Population 

In addition to ILI/ARI rates, semi-quantitative and only partly standardised indicators of intensity, geographic 
spread and trends of influenza activity are reported. 

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Influenza surveillance in Europe 2011–2012 

Each country assesses the intensity of clinical activity based on the historical data at its disposal. 

• 

• 

• 
• 

Low: no influenza activity or influenza activity is at baseline level. Usually, there will be a 6–12 week period 
in winter when the level of clinical influenza activity rises above the baseline threshold, but in the very 
occasional winter (perhaps 1 in 10), activity never gets above the baseline level. 
Medium: level of influenza activity usually seen when influenza virus is circulating in the country based on 
historical data. 
High: higher than usual influenza activity compared to historical data. 
Very high: influenza activity is particularly severe compared to historical data. 

The geographic spread can range from no activity, sporadic, local or regional to widespread activity: 

• 

• 

• 

• 

• 

No activity: reports indicate no evidence of influenza virus activity. Cases of ILI/ARI may be reported in 
the country but the overall level of clinical activity remains at baseline levels and influenza virus infections 
are not being laboratory-confirmed. Cases occurring in people recently returned from other countries are 
excluded. 
Sporadic: isolated cases of laboratory-confirmed influenza infection in a region, or an outbreak in a single 
institution (such as a school, nursing home or other institutional setting), with clinical activity remaining at 
or below baseline levels. Cases occurring in people recently returned from other countries are excluded. 
Local outbreak: increased ILI/ARI activity in local areas (such as a city, county or district) within a region, 
or outbreaks in two or more institutions within a region, with laboratory-confirmed cases of influenza 
infection. Levels of activity in remainder of region, and other regions of the country, remain at or below 
baseline levels. 
Regional activity: ILI/ARI activity above baseline levels in one or more regions with a population 
comprising less than 50% of the country’s total population, with laboratory-confirmed influenza infections in 
the affected region(s). Levels of activity in other regions of the country remain at or below baseline levels. 
Regional activity generally does not apply to countries with a population of less than 5 million, unless the 
country is large with geographically distinct regions. 
Widespread activity: ILI/ARI activity above baseline levels in one or more regions with a population 
comprising 50% or more of the country’s population, with laboratory-confirmed influenza infections. 

The trend is assessed by comparing current influenza activity with that in previous weeks and can be increasing, 
decreasing or stable. 

15