The World Health Organization's (WHO's) flu vaccine advisory group today recommended changing one strain—the 2009 H1N1 component—for the Northern Hemisphere's 2017-18 flu season, which mirrors a recommendation it made last September for the Southern Hemisphere's upcoming season.
Also, the advisors reviewed the latest genetic information about recent avian and other zoonotic flu viruses and recommended two new candidate vaccine viruses for H7N9 avian flu, plus three new ones for other potential pandemic threats.
Seasonal flu change
The new H1N1 vaccine strain, called A/Michigan/45/2015, replaces A/California/7/2009, which has been in use as a vaccine strain since the 2009 H1N1 virus became a regularly circulating seasonal flu strain after the 2009-10 pandemic. WHO advisors recommended it for the Southern Hemisphere's 2017 vaccine to improve protection against subclades that emerged last year.
Since September 2016, 2009 H1N1 has circulated at very low levels in most parts of the world, with most viruses belonging to subclade 6B.1, with a small portion of them in Asia and Oceana part of subclade 6B.2.
Though tests on ferret sera showed that most recent circulating viruses were antigenically similar to both the California and Michigan vaccine strains, tests using human sera hinted at a possible gap in protection from the California strain among the adult samples.
The WHO recommends the following for the Northern Hemisphere's trivalent vaccines:
- For H1N1, an A/Michigan/45/2015-like virus
- For H3N2, an A/Hong Hong/4801/2014-like virus
- For B, Brisbane/60/2008-like virus (belonging to the Victoria lineage)
For quadrivalent versions that contain two influenza B strains, the WHO experts recommended adding Phuket/3073/2013-like virus, a Yamagata lineage virus that is the second B component of quadrivalent vaccines for both the Southern Hemisphere's past and the Northern Hemisphere's current season.
H3N2 has been the dominant strain globally over the past several months, and the WHO said circulating viruses within the 3C2.a clade have become genetically diverse but remain antigenically similar to the current vaccine strain.
Five new pandemic candidate vaccine viruses
As vaccine advisors assess the need for new seasonal flu vaccine strains, they also look at the latest zoonotic influenza strains to see if any new candidate vaccine viruses are needed to assist with pandemic preparedness.
At a media telebriefing yesterday to address China's recent surge of H7N9 activity and recent genetic changes, officials said the virus has diverged into two distinct genetic groups, which would likely have implications for candidate vaccine viruses.
Today the group said that recent H7N9 viruses fall into the Yangtze River Delta (YRD) or Pearl River Delta (PRD) hemagglutinin lineages, and that two existing candidate vaccine viruses don't seem to protect against recent YRD-lineage viruses. They proposed a new candidate vaccine virus to protect against those viruses.
Also, they said the newly identified highly pathogenic H7N9 viruses isolated from poultry and people are genetically and antigenically distinct from other H7N9 viruses, including recommended candidate strain, including the newly proposed one. Therefore, the group recommended a new candidate vaccine virus to protect against the highly pathogenic H7N9 strain.
The group also recommended three other candidate pandemic vaccine viruses, two against recent variant H1N1 strains and one against the recent H5N6 virus circulating in Japan and South Korea.
US stockpile considerations
Changes in the H7N9 virus have prompted US officials to reassess the status of H7N9 vaccine in the US Strategic National Stockpile (SNS), Stat reported yesterday, quoting Rick Bright, PhD, who heads the Biomedical Advanced Research and Development Authority (BARDA).
Currently, the SNS hold enough H7N9 vaccine to protect 12 million people against the earlier H7N9 strain. Officials are anticipating that a new vaccine is needed, and BARDA will need to decide if they should procure a full order of vaccine to protect against newer H7N9 viruses or replenish supplies of the older vaccine, some of which has degraded and was discarded.
Another option would be to see of some H7N9 viruses cross-protect against both lineages, Bright told Stat.
Sep 29, 2016, CIDRAP News story "WHO switches H1N1 in Southern Hemisphere flu vaccine"
Mar 1 Stat story