Twice annually, the World Health Organization (WHO) organizes consultations with an advisory group of experts to analyse influenza virus surveillance data generated by the WHO Global Influenza Surveillance and Response System (GISRS), and issues recommendations on the composition of the influenza vaccines for the following influenza season.
On Thursday, WHO announced the recommended composition of influenza virus vaccines for use in the 2019-2020 northern hemisphere influenza season. It is recommended that egg based quadrivalent vaccines for use in the 2019-2020 northern hemisphere influenza season contain the following:
- an A/Brisbane/02/2018 (H1N1)pdm09-like virus;
- an A(H3N2) virus to be announced on 21 March 2019. In light of recent changes in the proportions of genetically and antigenically diverse A(H3N2) viruses, the recommendation for the A(H3N2) component has been postponed.
- a B/Colorado/06/2017-like virus (B/Victoria/2/87 lineage); and
- a B/Phuket/3073/2013-like virus (B/Yamagata/16/88 lineage).
It is recommended that the influenza B virus component of trivalent vaccines for use in the 2019-2020 northern hemisphere influenza season be a B/Colorado/06/2017-like virus of the B/Victoria/2/87-lineage.
Why is there a delay in selecting the A(H3N2) virus component of 2019-20 influenza vaccines? WHO explains:
Influenza A(H3N2) viruses have presented an increasing challenge for vaccine virus selection due to frequent changes in the virus and difficulties in generating candidate vaccine viruses for use in egg-based manufacturing. Experts at the consultation reviewed various sources of data including virus surveillance, antigenic characterization, and virus fitness forecasts, and identified multiple co-circulating influenza A(H3N2) virus groups. In recent months, the proportion of viruses in one antigenically distinct group has increased in many countries, prompting a delay in the selection of the A(H3N2) vaccine component. This delay will allow more time for monitoring virus circulation and characterisation of appropriate vaccine viruses.
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