World Health Organization (WHO) flu vaccine advisors met in Atlanta this week to recommend the seasonal influenza strains to include in the Southern Hemisphere's 2019 vaccine and recommended swapping out the H3N2 component in egg-based vaccines.
The group also reviewed the latest information about zoonotic flu viruses and recommended three new candidate vaccine viruses for pandemic preparedness.
H3N2 switch for egg-based vaccines
According to a report released yesterday at the end of the meeting, the WHO recommends the following for the Southern Hemisphere's egg-based quadrivalent (four-strain) vaccines:
- For H1N1, an A/Michigan/45/2015-like virus
- For H3N2, an A/Switzerland/8060/2017)-like
- For B Victoria, a B/Colorado/06/2017-like virus
- For B Yamagata, a B/Phuket/3073/2013-like virus
For egg-based trivalent versions that have only one B strain, the experts recommended including the Victoria lineage vaccine virus (B/Colorado/06/2017-like). And for non-egg based vaccines, they recommended the same H3N2 component used during the Southern Hemisphere's 2018 vaccine and the Northern Hemisphere's 2018-2019 vaccine—an A/Singapore/INFIMH-16-0019/2016-like virus.
In deciding what strains to recommend, the group focused on flu activity between February and September, which saw circulation of all three strains. However, influenza A was predominant in most countries, with cocirculation of 2009 H1N1 and H3N2 viruses in all parts of the world, though higher proportions of 2009 H1N1 were seen in Africa, most of Asia, tropical South America, Central America, Oceania, and the Caribbean.
For H3N2, higher proportions circulated in some temperate South American regions, southern Asia, North America, and northern Europe.
Regarding influenza B, higher proportions were seen in Europe, western Asia, and Canada. Globally, the Yamagata lineage predominated, but Victoria lineage viruses also circulated during the same period.
Most circulating 2009 H1N1 viruses belonged to the 6B.1 genetic subclade and were genetically indistinguishable from the vaccine virus strain. For H3N2, 3C.2a2 was the predominant circulating subclade, and most recent viruses were well inhibited by ferret sera raised against last season's cell-culture–propagated vaccine strain.
Last year's egg-propagated vaccine strain inhibited a smaller portion of current H3N2 viruses, but the new A/Switzerland/8060/2017 vaccine strain inhibited the majority tested from the predominant subclade.
Trio of new pandemic candidate viruses
The vaccine advisors also reviewed zoonotic flu virus activity and looked at results from genetic characterization of recent samples to see if any new candidate vaccine viruses are needed for pandemic preparedness.
Since they last met in February, one human H5N6 case and one human H9N2 case were reported in China. Also, 13 variant H1N2 (H1N2v) cases were reported in the United States, 12 of them in people who were exposed to swine or attended an agricultural fair.
Based on their review, they recommended one new H5N1 virus (A/duck/Bangladesh/17D1012/2018-like), a new H9N2 virus (A/Anhui-Lujiang/39/2018-like), and a new H1N2v virus (A/Michigan/383/2018-like).
Sep 27 WHO recommendations for 2019 Southern Hemisphere seasonal flu vaccine strains
Feb 22 CIDRAP News story "WHO changes 2 strains for 2018-19 flu vaccine"