Flu transmission has plummeted amid the COVID-19 pandemic, potentially causing two virus strains to disappear. This reduced diversity could enable more precise vaccine formulations.
Influenza, caused by RNA viruses in the Orthomyxoviridae family, is a seasonal illness peaking in autumn and winter in temperate regions. Globally, it claims 290,000 to 650,000 lives annually.
As anticipated, flu cases have sharply declined recently, largely due to mask-wearing and other barrier measures implemented against COVID-19, experts note.
Notably, two strains have evaded detection for over a year, according to STAT News.
Seasonal flu in humans stems from influenza A and B viruses. Influenza A subtypes are defined by hemagglutinin (H) and neuraminidase (N) surface proteins.
The dominant human subtypes are H1N1 and H3N2, with H3N2 showing greater clade diversity than H1N1.
Influenza B lacks subtypes but splits into B/Yamagata and B/Victoria lineages.
STAT reports that the 3c3.A clade of H3N2 and the B/Yamagata lineage have not been detected since March 2020.
“I think there's a good chance it's gone. But the world is wide,” says Trevor Bedford of the Fred Hutchinson Cancer Research Center in Seattle, regarding H3N2.
“Just because no one saw it doesn't mean it's gone. But it could have disappeared,” adds Florian Krammer of the Icahn School of Medicine at Mount Sinai in New York, on B/Yamagata.
Richard Webby, WHO expert on influenza ecology in animals and birds, acknowledges a major drop in viral diversity but believes these strains persist at low levels.
Whether these strains are truly extinct remains uncertain. If confirmed, it could simplify vaccine targeting for health authorities.
Annual flu persists due to viral mutations evading immunity, with H3N2 particularly diverse.
Epidemiologists select prevalent strains for yearly vaccines. A universal vaccine would be ideal but is not yet available.
