On 19-21 February 2018 in Geneva, the World Health Organization (WHO) has agreed on the recommended composition of the trivalent influenza vaccine for the northern hemisphere 2018-2019 influenza season as:
- an A/Michigan/45/2015 (H1N1)pdm09-like virus;
- an A/Singapore/INFIMH-16-0019/2016 (H3N2)-like virus;
- a B/Colorado/06/2017-like virus (B/Victoria/2/87 lineage).
For quadrivalent vaccines containing two influenza B viruses, also a B/Phuket/3073/2013-like virus is recommended.
The WHO recommendations are made with a knowledge of the currently circulating viruses globally. WHO recommended two changes, compared to the current trivalent and quadrivalent vaccines for the 2017–2018 season in the northern hemisphere influenza season. Similar to the 2018 southern hemisphere vaccine, the A(H3N2) component was changed to an A/Singapore/INFIMH-16-0019/2016 (H3N2)-like virus. In trivalent vaccines the B component was switched to a B/Victoria -lineage B/Colorado/06/2017-like virus, representing the emergent strain of B/Victoria with the amino acid deletions Δ162-163 in haemagglutinin (HA). The A(H1N1)pdm09 component in trivalent and quadrivalent vaccines and the B/Yamagata component in quadrivalent vaccines remained the same.
Almost all of the currently circulating A(H1N1)pdm09 viruses were antigenically indistinguishable from the current vaccine virus A/Michigan/45/2015, and the same component remained the same.
Almost all of the currently circulating A(H3N2) viruses belonged to the HA phylogenetic clade 3C.2a. WHO recommended the inclusion of a A/Singapore/INFIMH-160019/2016-like virus that belongs to the 3C.2a1 subclade. Recent A(H3N2) viruses were better inhibited by antisera raised against this egg-propagated virus, compared to antisera raised against the egg-propagated A/Hong Kong/4801/2014, which is the current 2017-2018 A(H3N2) vaccine component.
Globally, both B virus lineages continue to co-circulate with B/Yamagata lineage largely predominating. The B/Yamagata component was only included in the 2017-2018 quadrivalent vaccine, while all of the circulating B/Yamagata/16/88 lineage viruses were well inhibited by antisera raised against B/Phuket/3073/2013. The same component was retained for the quadrivalent 2018-2019 vaccine.
WHO recommended now the inclusion of the B/Victoria lineage into the trivalent vaccine for the northern hemisphere 2018-2019 influenza season. The recommended vaccine virus B/Colorado/06/2017 belongs to clade 1A and carries the characteristic two amino acid deletions K162 and N163 in HA. Though the level of detection of B/Victoria viruses remain low, a substantial and increasing proportion carries this deletion.
Further antigenic and genetic characteristics of recent seasonal influenza viruses are described in the full report of the recommendation.
