WHO releases recommendations for the 2019–2020 northern hemisphere seasonal influenza vaccine

WHO’s recommendations for the composition of influenza virus vaccines for use in the 2019–2020 northern hemisphere influenza season have now been released.

Due to the constantly evolving nature of influenza viruses, the compositions of viruses in influenza vaccines need to be revised periodically. Consequently, WHO holds 2 annual consultations – 1 for the northern hemisphere and 1 for the southern hemisphere – to analyse influenza virus surveillance data generated by the WHO Global Influenza Surveillance and Response System (GISRS), and to recommend the composition of the influenza vaccines for the following influenza season.

The recommendations are then used by the national vaccine regulatory agencies and the pharmaceutical companies to develop, produce and license influenza vaccines.

European Region’s contribution to developing the best possible influenza vaccine

These recommendations were made possible by national influenza centres (NICs), which detect and characterize viruses and share them with WHO collaborating centres for in-depth analyses. During the annual consultation an advisory group of experts analyses the data provided by the countries to recommend the new compositions. This year, NICs in the WHO European Region have tested more than 360 000 clinical specimens and detected 57 443 influenza viruses. NICs in 44 countries of the Region shared viruses which were included in the data analysed, and which resulted in the new recommendations.

Changes to previous season’s recommendations

Two types of influenza virus cause illness in humans, type A and type B. While no changes are recommended for the influenza B virus components, the recommendation for the A(H1N1) virus component has been changed. The A/Michigan/45/2015 (H1N1)pdm09-like virus included in the 2018–2019 vaccine composition is replaced by an A/Brisbane/02/2018 (H1N1)pdm09-like virus from the subclade 6B.1A, which is now predominant globally.

Final composition

WHO’s recommendations for the composition of influenza virus vaccines for use in the 2019–2020 northern hemisphere influenza season are as follows:

  • an A/Brisbane/02/2018 (H1N1)pdm09-like virus
  • an A(H3N2) virus to be announced on 21 March 2019*
  • a B/Colorado/06/2017-like virus (B/Victoria/2/87 lineage)
  • a B/Phuket/3073/2013-like virus (B/Yamagata/16/88 lineage).

The first 3 of these are recommended virus strains for inclusion in trivalent influenza vaccines, and the last is a recommended additional virus strain for inclusion in quadrivalent influenza vaccines.

The WHO Consultation and Information Meeting on the Composition of Influenza Virus Vaccines for Use in the 2019–2020 Northern Hemisphere Influenza Season took place on 18–21 February in Beijing, China.

Vaccination – the most effective measure to prevent severe disease caused by influenza

Interim results on vaccine effectiveness suggest that, in the 2018–2019 season, vaccination reduced the risk of medically attended influenza by at least half in the northern hemisphere, and this result was even better in children.

Influenza vaccines are safe and the principal measure for preventing influenza and reducing the impact of epidemics. WHO recommends that health-care workers and people who are most at risk of developing serious complications from influenza infection – the elderly, people with chronic conditions, pregnant women and young children – be vaccinated every year before the season begins.

*Selection of the A(H3N2) virus component of 2019–2020 influenza vaccines has been delayed. Influenza A(H3N2) viruses have presented an increasing challenge for vaccine virus selection due to both the frequent changes in the virus itself and the difficulties in generating candidate vaccine viruses to be used in egg-based manufacturing of the vaccines. In recent months, the proportion of viruses in 1 antigenically distinct group has increased in many countries. This delay will allow more time for monitoring virus circulation and characterization of appropriate vaccine viruses.

Countries in Region that shared influenza viruses with a WHO collaborating centre