World Health Organization recommendations for the influenza virus vaccine composition for the 2020 southern hemisphere season

ECDC comment

On September 2019, WHO has agreed on the recommended composition of the quadrivalent and trivalent influenza vaccines for the southern hemisphere 2020 influenza season.

The World Health Organization (WHO) convenes in February and September each year to recommend influenza viruses for inclusion in the vaccines for the northern and southern hemisphere seasons, respectively. In September 2019, WHO agreed on the recommended composition of the quadrivalent influenza vaccine for the southern hemisphere 2020 influenza season [1]. The recommended vaccine virus components are:

  • an A/Brisbane/02/2018 (H1N1)pdm09-like virus
  • an A/South Australia/34/2019 (H3N2)-like virus
  • a B/Washington/02/2019-like (B/Victoria lineage) virus
  • a B/Phuket/3073/2013-like (B/Yamagata lineage) virus

It was recommended that trivalent vaccines for use in the 2020 southern hemisphere influenza season have the same components, without the B/Phuket/3073/2013-like (B/Yamagata/16/88 lineage) virus. 

WHO recommended three changes, compared to the 2019 southern hemisphere quadrivalent and trivalent vaccines. The A(H1N1)pdm09, A(H3N2) and B/Victoria components for trivalent and quadrivalent vaccines were changed, while the  B/Yamagata component for the quadrivalent vaccines remained the same. For the 2020 season, the B/Victoria-lineage virus was again recommended for inclusion in the trivalent vaccines for the southern hemisphere.

ECDC comment

WHO’s influenza vaccine recommendations are based on the knowledge of the viruses currently circulating worldwide. 

Similar to the recommendation for the 2018–2019 northern hemisphere vaccine [3], WHO recommended changing the A(H1N1)pdm09 virus component for the southern hemisphere 2020 influenza season to A/Brisbane/02/2018. Although the 2019 vaccine component A/Michigan/45/2015 A(H1N1)pdm09 remains close to the circulating A(H1N1)pdm09 viruses in its genetic and antigenic characteristics, serological studies showed that a virus component representing the widely circulating 6B.1A subgroup with S193P amino acid substitution in HA would be more appropriate. 

WHO recommended changing the A(H3N2) virus component for the southern hemisphere 2020 influenza season to A/South Australia/34/2019, which belongs to subclade 3C.2a1b. Genetic analyses of circulating A(H3N2) viruses showed that they have undergone considerable genetic diversification of their HA gene and the majority fell in the 3C.2a1b subclade. 

Both B viruses circulated at low levels during 2018–2019. WHO recommended the inclusion of the B/Victoria lineage in the trivalent vaccine for the southern hemisphere 2020 influenza season. All circulating B/Victoria viruses belonged to clade 1A but were genetically and antigenically diverse. The majority of characterised viruses belonged to a group that carried three amino acid deletions (Δ162-164) in HA like the recommended vaccine virus B/Washington/02/2019. However, in some countries (e.g. Madagascar, Mozambique and many countries in Central and South America), B/Victoria viruses belonging to a group carrying two deletions (Δ162-163) in HA were more frequent during the past season. B/Yamagata viruses all fell in clade 3 and remained similar to the quadrivalent vaccine virus B/Phuket/3073/2013, so the same virus was retained in the southern hemisphere 2020 vaccine. 

Further antigenic and genetic characteristics of recent seasonal influenza viruses are described in the full report of the recommendation [1].