Global circulation of respiratory viruses: from local observations to global predictions
Authors: Jean-Michel Heraud, Norosoa Harline Razanajatovo, Cecile Viboud
Journal: The Lancet Global Health (2019)

The seasonality of respiratory viruses remains a challenging question for surveillance systems; robust information on viral circulation is crucial to optimise public health interventions, especially in low-income and middle-income countries where disease burden is highest. Influenza viruses, respiratory syncytial viruses (also known as human orthopneumoviruses), parainfluenza viruses, and human metapneumovirus account for most acute viral respiratory infections, particularly among children aged 5 years and younger and older people (65 years and older).1Shi T McLean K Campbell H Nair H Aetiological role of common respiratory viruses in acute lower respiratory infections in children under five years: a systematic review and meta-analysis.J Glob Health. 2015; 5010408 Crossref PubMed Scopus (119) Google Scholar In The Lancet Global Health, You Li and colleagues2Li Y Reeves RM Wang X et al.Global patterns in monthly activity of influenza virus, respiratory syncytial virus, parainfluenza virus, and metapneumovirus: a systematic analysis.Lancet Glob Health. 2019; 7: e1031-e1045Summary Full Text Full Text PDF PubMed Scopus (120) Google Scholar provide the first comprehensive analysis of the global seasonality of these four most common viruses. Through a systematic analysis of published and unpublished studies, and publicly available surveillance data, the authors model the global circulation of these viruses in 246 locales and explore the climatic drivers of seasonality. Li and colleagues' modelling approach relies on estimating the fraction of viruses circulating in each month of the year, in line with previous work.3Caini S Andrade W Badur S et al.Temporal patterns of influenza A and B in tropical and temperate countries: what are the lessons for influenza vaccination?.PLoS One. 2016; 11e0152310 PubMed Google Scholar They find marked influenza virus seasonality in temperate regions of the northern and southern hemispheres and weaker seasonality closer to equator.2Li Y Reeves RM Wang X et al.Global patterns in monthly activity of influenza virus, respiratory syncytial virus, parainfluenza virus, and metapneumovirus: a systematic analysis.Lancet Glob Health. 2019; 7: e1031-e1045Summary Full Text Full Text PDF PubMed Scopus (120) Google Scholar, 4Obando-Pacheco P Justicia-Grande AJ Rivero-Calle I et al.Respiratory syncytial virus seasonality: a global overview.J Infect Dis. 2018; 217: 1356-1364Crossref PubMed Scopus (116) Google Scholar, 5Viboud C Alonso WJ Simonsen L Influenza in tropical regions.PLoS Med. 2006; 3: e89Crossref PubMed Scopus (334) Google Scholar Influenza virus epidemics occur later in the year with increasing latitude, whereas a notable westward wave of infection is identified across Europe. By contrast, respiratory syncytial virus seasonality is well defined throughout the globe,2Li Y Reeves RM Wang X et al.Global patterns in monthly activity of influenza virus, respiratory syncytial virus, parainfluenza virus, and metapneumovirus: a systematic analysis.Lancet Glob Health. 2019; 7: e1031-e1045Summary Full Text Full Text PDF PubMed Scopus (120) Google Scholar hinting at a stronger influence of environmental factors on the transmission of respiratory syncytial virus than on the transmission of influenza virus. Further statistical analyses suggest a complex interplay between temperature and humidity in driving influenza virus and respiratory syncytial virus epidemic patterns globally.2Li Y Reeves RM Wang X et al.Global patterns in monthly activity of influenza virus, respiratory syncytial virus, parainfluenza virus, and metapneumovirus: a systematic analysis.Lancet Glob Health. 2019; 7: e1031-e1045Summary Full Text Full Text PDF PubMed Scopus (120) Google Scholar However, it can be difficult to disentangle the effect of these variables due to collinearity, and although experimental animal models support an effect of absolute humidity on influenza transmission, no comparable model exists for respiratory syncytial virus. Little is known about seasonality of parainfluenza virus and metapneumovirus. In the present study,2Li Y Reeves RM Wang X et al.Global patterns in monthly activity of influenza virus, respiratory syncytial virus, parainfluenza virus, and metapneumovirus: a systematic analysis.Lancet Glob Health. 2019; 7: e1031-e1045Summary Full Text Full Text PDF PubMed Scopus (120) Google Scholar parainfluenza virus activity is more pronounced in spring and summer months in both hemispheres, whereas metapneumovirus predominates in late winter in temperate regions. Parainfluenza virus seasonality is further complicated by intriguing interactions between serotypes affecting the transmission dynamics of this virus (eg, between parainfluenza virus-1 and parainfluenza virus-3), which remain poorly understood. Broadly, analyses of parainfluenza virus and influenza virus2Li Y Reeves RM Wang X et al.Global patterns in monthly activity of influenza virus, respiratory syncytial virus, parainfluenza virus, and metapneumovirus: a systematic analysis.Lancet Glob Health. 2019; 7: e1031-e1045Summary Full Text Full Text PDF PubMed Scopus (120) Google Scholar, 6Yu H Alonso WJ Feng L et al.Characterization of regional influenza seasonality patterns in China and implications for vaccination strategies: spatio-temporal modeling of surveillance data.PLoS Med. 2013; 10e1001552 Crossref PubMed Scopus (176) Google Scholar illustrate how different strains of the same virus can have different timings of activity. These differences are likely to be driven by non-climatic factors,7Martinez ME The calendar of epidemics: seasonal cycles of infectious diseases.PLoS Pathog. 2018; 14e1007327 Crossref Scopus (87) Google Scholar including epidemiology (eg, mean age at infection, driving the relationship with school terms), population immunity, evolutionary dynamics, viral migrations, and competition with other subtypes and other pathogens. A major area for future work is to understand how climatic and non-climatic factors modulate the seasonality of respiratory viruses. Li and colleagues2Li Y Reeves RM Wang X et al.Global patterns in monthly activity of influenza virus, respiratory syncytial virus, parainfluenza virus, and metapneumovirus: a systematic analysis.Lancet Glob Health. 2019; 7: e1031-e1045Summary Full Text Full Text PDF PubMed Scopus (120) Google Scholar should be commended for amassing such a large amount of observations on the seasonality of respiratory viruses. The authors use a sensitive inclusion criterion, targeting any study reporting viral activity for more than 12 consecutive months. Although 1 year might be too short to fully capture the interannual variability of viral activity, this choice allows for a more inclusive description of global circulation patterns. Availability of longer time series would allow for analysis of multiyear epidemic cycles that might further illuminate the role of seasonal drivers. Armed with their predictive model, the authors provide a useful web tool to predict epidemic months of influenza virus and respiratory syncytial virus.2Li Y Reeves RM Wang X et al.Global patterns in monthly activity of influenza virus, respiratory syncytial virus, parainfluenza virus, and metapneumovirus: a systematic analysis.Lancet Glob Health. 2019; 7: e1031-e1045Summary Full Text Full Text PDF PubMed Scopus (120) Google Scholar This tool should be used with caution as it does not replace local surveillance information. Madagascar offers an interesting testbed for the tool, as influenza virus activity has been shown to be particularly irregular in this country, with little association with climate or travel.8Alonso WJ Guillebaud J Viboud C et al.Influenza seasonality in Madagascar: the mysterious African free-runner.Influenza Other Respir Viruses. 2015; 9: 101-109Crossref Scopus (17) Google Scholar We find that the influenza virus predictions do not align with observations in Madagascar (figure). By contrast, respiratory syncytial virus has well defined seasonality with peaks occurring in the first quarter of the year—Li and colleagues' predictions lag the observations. Although the unique situation of countries such as Madagascar will not affect the global circulation of respiratory virus, it exemplifies the need for tropical countries, particularly insular systems, to collect their own data to guide local control strategies, such as routine influenza vaccination and respiratory syncytial virus prophylaxis.3Caini S Andrade W Badur S et al.Temporal patterns of influenza A and B in tropical and temperate countries: what are the lessons for influenza vaccination?.PLoS One. 2016; 11e0152310 PubMed Google Scholar, 9Guillebaud J Heraud JM Razanajatovo NH Livinski AA Alonso WJ Both hemispheric influenza vaccine recommendations would have missed near half of the circulating viruses in Madagascar.Influenza Other Respir Viruses. 2017; 11: 473-478Crossref Scopus (3) Google Scholar Tools such as that developed by Li and colleagues will be particularly useful if they can be continuously updated as more information becomes available and model predictions are improved. In the coming years, low-income and middle-income countries will probably introduce new and improved vaccines to reduce morbidity and mortality due to major respiratory pathogens. In addition to increased seasonality information, a comprehensive understanding of the transmission dynamics of respiratory viruses will be important to project vaccine benefits, support cost-effectiveness studies, and inform local decision making. In the meantime, disease surveillance needs to be strengthened across a range of respiratory pathogens, facilitated by novel technologies, such as metagenomic, and real-time and next-generation sequencing methods, which are becoming more affordable and could be implemented in low-income and middle-income countries. Predictive models are very useful but do not alleviate the need for continued investments in surveillance to generate data, improve preparedness and early detection of emerging infections, elucidate the global transmission and evolutionary dynamics of respiratory viruses, and monitor antiviral resistance and vaccine escape.10Tang JW Lam TT Zaraket H et al.Global epidemiology of non-influenza RNA respiratory viruses: data gaps and a growing need for surveillance.Lancet Infect Dis. 2017; 17: e320-e326Summary Full Text Full Text PDF PubMed Scopus (64) Google Scholar We declare no competing interests. This report does not necessarily represent the views of the Institut Pasteur de Madagascar, the National Institutes of Health, or the US Government. Global patterns in monthly activity of influenza virus, respiratory syncytial virus, parainfluenza virus, and metapneumovirus: a systematic analysisThis study is the first to provide global representations of month-by-month activity of influenza virus, respiratory syncytial virus, parainfluenza virus, and metapneumovirus. Our model is helpful in predicting the local onset month of influenza virus and respiratory syncytial virus epidemics. The seasonality information has important implications for health services planning, the timing of respiratory syncytial virus passive prophylaxis, and the strategy of influenza virus and future respiratory syncytial virus vaccination. Full-Text PDF Open Access