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WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza, 

Influenza Division, National Center for Immunization and Respiratory Diseases

Update on Influenza B/Yamagata 

Surveillance

Rebecca Kondor, PhD

Interim Director, WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza

Lead, Genomics Analysis Team

Virology, Surveillance and Diagnosis Branch – Influenza Division – NCIRD
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WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza, 

Influenza Division, National Center for Immunization and Respiratory Diseases

WHO’s Global Influenza Surveillance and Response System (GISRS)

The mission of GISRS is to protect people from 

the threat of influenza by continuously 

functioning as a:

• Global mechanism of surveillance, 

preparedness and response for seasonal, 

pandemic and zoonotic influenza

• Global platform for monitoring influenza 

epidemiology and disease

• Global alert for novel influenza viruses and 

other respiratory pathogens

WHO GISRS
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WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza, 

Influenza Division, National Center for Immunization and Respiratory Diseases

• GISRS National Influenza Centers (NICs) 

• Collect respiratory specimens from 

established networks of physicians, health 

care centers or other sentinel sites, 

and/or they solicit influenza virus-positive 

samples 

• Perform initial influenza virus detection, 

typing and subtyping

• CDC develops and manufactures 

assays which are distributed by IRR

• Share a subset of representative influenza 

virus specimens and/or isolates with 

WHO CCs for antigenic and genetic 

characterization and creation of 

candidate vaccine viruses

• Report to WHO RespiMart

• epidemiological information FluID

• laboratory results to FluNet

152 WHO National Influenza Centers in 129 Member States

• 7 WHO Collaborating Centers for Influenza 

• 4 Essential Reference Laboratories 

• 12 WHO H5 Reference Laboratories

WHO’s Global Influenza Surveillance and Response System (GISRS)

WHO GISRS
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WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza, 

Influenza Division, National Center for Immunization and Respiratory Diseases

WHO GISRS

Update on Influenza B/Yamagata Surveillance 

FluNet data can be delineated by surveillance site type

• Sentinel – Sentinel surveillance systems collect high-quality data in a timely manner, systematically and routinely 

from sentinel surveillance sites representative of the population under surveillance. Case definition (ILI, SARI, ARI) 

and populations differ by country (e.g., only certain age groups, health-care workers, hospitalized)

• Non-sentinel – Data reported in this category may include outbreak investigation, universal testing, testing at point 

of care or other systems apart from sentinel surveillance

• Type not defined – These data may include sentinel or non-sentinel surveillance sources or both

The level of information reported to FluNet depends on the country and the laboratory where testing occurs

• Rapid tests only determine influenza A or B

• Large clinical and hospital laboratories often only determine influenza A or B, with some assays also determining 

influenza A subtype

• A higher proportion of viruses from sentinel surveillance will include influenza A and B subtyping results

WHO GISRS
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WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza, 

Influenza Division, National Center for Immunization and Respiratory Diseases

Types of Assays for B/lineage at NIC:

• Serology Based

• CDC WHO Kit 

• anti-B/Vic and anti-B/Yam goat antiserum – created by WHO CC Atlanta available in CDC IRR

• 52 countries recently ordered kits

• HI Assay–anti-B/Vic and anti-B/Yam ferret antiserum provided by WHO CCs

• Molecular Based

• CDC RT-PCR B Lineage Assay RUO - created by WHO CC Atlanta available in CDC IRR

• 104 countries recently ordered kits

• Other RT-PCR assays

• Sequencing (sanger or NGS) – clinical specimens or viral isolates

GISRS NICs also submit specimens to WHO CCs for virus characterization

• Using the above methods B lineage is attempted for all viruses received

• WHO CC have confirmed ZERO circulating B/Yamagata lineage viruses collected after March 2020

• Those reported as B/Yamagata were determined to be incorrectly lineage reports, negative for influenza 

or B/Yamagata component of LAIV

Non-sentinel surveillance may use different assays than those listed above. WHO GISRS

WHO GISRS

Update on Influenza B/Yamagata Surveillance 
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WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza, 

Influenza Division, National Center for Immunization and Respiratory Diseases

WHO GISRS Influenza Surveillance 

September 2017- August 2020

Northern Hemisphere

Southern Hemisphere

• Influenza B/Yamagata lineage viruses were the 

predominant B/lineage circulating during the 

2017-18 Northern Hemisphere and 2018 

Southern Hemisphere seasons

• 2018-2019 Northern Hemisphere had much less 

B activity overall and B/Victoria lineage viruses 

predominated

• 2019 Southern Hemisphere showed regional 

differences in B/lineage circulation with 

B/Yamagata mainly circulating in South America

• 2019-20 Northern Hemisphere season began 

with an early B/Victoria lineage peak, followed 

by A(H1N1)pdm09

• COVID-19 Pandemic and its mitigation saw a 

drop in influenza virus detection and circulation

GIP FLUNET PowerBI
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WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza, 

Influenza Division, National Center for Immunization and Respiratory Diseases

WHO GISRS Influenza Surveillance 

September 2020- August 2023

Northern Hemisphere

Southern Hemisphere

• GISRS NICs continued influenza surveillance 

during the COVID-19 Pandemic

• Influenza continued to be detected but without 

seasonal peaks in epidemics until late 2021

• All influenza B activity due to B/Victoria lineage

• February 1 – August 31, 2023

• 1/3 of all viruses detected by GISRS were 

influenza B

• Parts of Northern Hemisphere saw second peak 

of activity due to B/Victoria and A(H1N1)pdm09 

viruses

• Southern Hemisphere 2023 season co-circulation 

of B/Victoria and A(H1N1)pdm09 viruses

GIP FLUNET PowerBI
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WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza, 

Influenza Division, National Center for Immunization and Respiratory Diseases

Countries reporting influenza B detections to FluNet February 1- August 31, 2023 All Types of Surveillance

Map made from data available at GIP FLUNET PowerBI
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WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza, 

Influenza Division, National Center for Immunization and Respiratory Diseases

Virus Detections by B lineage reported to FluNet

All Types of Surveillance

Data source: GIP FLUNET PowerBI

1 B/Yamagata reported (non-sentinel surveillance)

1 February 2023 through 31 August 2023

1 B/Yam non-sentinel surveillance
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WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza, 

Influenza Division, National Center for Immunization and Respiratory Diseases

Virus Detections by subtype reported to FluNet

Sentinel Surveillance

Data source: GIP FLUNET PowerBI

No B/Yamagata detected in GISRS sentinel surveillance

1 February 2023 through 31 August 2023
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WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza, 

Influenza Division, National Center for Immunization and Respiratory Diseases

WHO GISRS Influenza B/Lineage Reports

February 1 – August 31, 2023

As of 31 August 2023

• 99,453 influenza B viruses detected in 139 countries

• 15,878 influenza B viruses had results from B/lineage assays reported to FluNet from all surveillance 

types

• 15 initial reports to GISRS as B/Yamagata underwent confirmation by WHO CCs and WHO Global 

Influenza Programme

• 13 were confirmed as B/Victoria Lineage or negative for influenza and their FluNet records were 

updated accordingly

• 2 did not have specimens available for confirmation testing at a WHO CC (one was not reported 

to FluNet). These specimens did not yield viral isolates or sequence data.

• All influenza B viruses received by WHO CCs were B/Victoria lineage

• Genomic surveillance of influenza B viruses found only genet segments derived from circulating 

B/Victoria lineage

• This data supports that B/Yamagata viruses are extremely rare and not responsible for recent epidemics

• The majority of B/Yamagata reports are due to an incorrect lineage determination
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WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza, 

Influenza Division, National Center for Immunization and Respiratory Diseases

WHO vaccine recommendations for the 

Southern Hemisphere 2024

WHO recommendation and technical reports available on the WHO web site: https://www.who.int/teams/global-influenza-programme/vaccines/who-recommendations 

It is recommended that vaccines licensed for use in the 2024 southern hemisphere influenza season 

contain the following:

Trivalent: Egg-based Vaccines

- an A/Victoria/4897/2022 (H1N1)pdm09-like virus antigen*; 

- an A/Thailand/8/2022 (H3N2)-like virus antigen**; and 

- a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.

Trivalent: Cell- or recombinant-based Vaccines 

- an A/Wisconsin/67/2022 (H1N1)pdm09-like virus antigen*; 

- an A/Massachusetts/18/2022 (H3N2)-like virus antigen**; and

- a B/Austria/1359417/2021 (B/Victoria lineage)-like virus antigen.

Quadrivalent: egg- or cell culture- or recombinant-based vaccines

- Above 3 components; and a B/Phuket/3073/2013 (B/Yamagata lineage)-like antigen.

* Different from that recommended for the 2023 southern hemisphere season but the same as the NH 2023-24 recommendation.

** Different from that recommended for the 2023 southern hemisphere season and from NH 2023-24 recommendation.
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WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza, 

Influenza Division, National Center for Immunization and Respiratory Diseases

WHO Vaccine Recommendations Summary

• The absence of confirmed detection of naturally occurring B/Yamagata lineage viruses is 

indicative of very low risk of infection by B/Yamagata lineage viruses. 

• While influenza vaccines are safe and effective, the manufacture and use of inactivated and 

live attenuated vaccines containing B/Yamagata lineage viruses pose a theoretical risk of 

reintroduction of B/Yamagata lineage virus into the population. This risk can be mitigated by 

the removal of B/Yamagata lineage viruses from the vaccines. 

• It was the opinion of the WHO influenza vaccine composition advisory committee that the 

inclusion of a B/Yamagata antigen as a component of influenza vaccines is no longer 

warranted, and every effort should be made to exclude this component as soon as practically 

possible. 

• The committee recognizes that national or regional authorities are responsible for approving 

the composition and formulation of vaccines used in each country and should consider the 

use & relative benefit(s) of trivalent or quadrivalent influenza vaccines.
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WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza, 

Influenza Division, National Center for Immunization and Respiratory Diseases

Ongoing Influenza B Surveillance 

• GISRS laboratories will continue to be supported by CDC for influenza testing, typing 

and influenza A/B subtyping through reagents available in IRR

• GISRS laboratories and WHO CCs will continue to perform B/lineage testing

• Any reports of B/Yamagata viruses will be confirmed by WHO CCs

• For the 2023-2024 season, US public health labs will continue to perform assays to 

determine B/lineage– all B/Yamagata detections will be sent to CDC for confirmation.

• All US specimens with RT-PCR results of a mix of influenza A and B will also be sent to 

CDC for confirmation. The majority of previous results of A/B mixtures were from 

individual vaccinated with LAIV.
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WHO Collaborating Center for Surveillance, Epidemiology and Control of Influenza, 

Influenza Division, National Center for Immunization and Respiratory Diseases

Support and Disclaimer

The findings and conclusions in this report are those of the authors and do not necessarily represent 

the official position of the Centers for Disease Control and Prevention.

These projects have been funded in part with federal funds from US Health and Human 

Services (National Institutes of Health, Centers for Disease Control, and the Biomedical 

Advanced Research and Development Authority).