A line of the flu virus has been effectively wiped out, ironically thanks to COVID-19.
The ‘Yamagata’ lineage is one of two varieties of Influenza B, which along with Influenza A subtypes, causes seasonal flu.
But no evidence of the Yamagata lineage has been detected globally since the outbreak of SARS-CoV-2 – the virus that causes COVID-19 – and the United States Food and Drug Administration has agreed with recommendations from the World Health Organization that it no longer be included in seasonal flu vaccines.
Yamagata was already in decline pre-pandemic, but none of its strains have been isolated since March 2020. It’s believed containment measures introduced to prevent the spread of COVID-19 – such as face masking and physical isolation – may have helped to drive Yamagata to undetectable levels.
Last year, the WHO recommended only one Yamagata lineage be included in quadrivalent southern hemisphere seasonal flu vaccines. Its recent update for the 2024-25 northern hemisphere flu season said the inclusion of Yamagata-like viruses in trivalent jabs was “no longer warranted”.
Now, a meeting by the FDA’s Vaccines and Related Biological Products Advisory Committee on Tuesday (local time) has ratified that recommendation. In a statement, the FDA said:
“In the interest of public health, FDA strongly recommended to influenza vaccine manufacturers the removal of the B/Yamagata lineage virus from seasonal influenza vaccines in the U.S. for the 2024-2025 influenza season. FDA and the manufacturers have been working together so that the move from quadrivalent to trivalent seasonal influenza vaccines occurs for the upcoming influenza season.”
The United States’ next batch of flu vaccines will include components of two Influenza A viruses and one ‘Victoria’ lineage Influenza B virus.
Before the WHO and FDA announced their new directions, the August meeting of Australia’s Advisory Committee on Vaccines discussed the potential for removing the Yamagata lineage from future inoculations.
Options to make a stronger vax
Robert Booy, an infectious diseases paediatrician at The Children’s Hospital at Westmead, tells Cosmos Yamagata was highly unlikely to return, but that its disappearance merely emphasises the competition between respiratory viruses in the environment.
“The high likelihood is that Yamagata is gone,” Booy says.
“The four years of non-appearance has only year-on-year reinforced the understanding that there are a lot of other viruses out there competing for the biological niche in humans and this one has lost its way.”
While he agrees with the decision by the WHO, FDA, and likely Australia’s TGA, to adopt a ‘three-pronged’ flu vaccine for the future, he says there could be an opportunity to stick with a four-antigen jab that gives greater protection against the most potent ‘A’ subtypes.
“Influenza H3N2, which first appeared more than 50 years ago from the Hong Kong pandemic in 1962, is the most predominant cause of influenza and it continues to mutate and evolve and change so that our vaccines, even though they’re decided upon in the 6-12 months before they’re introduced, still only provide 50-70% protection,” Booy says.
“Some people therefore think that if we go for two different variants of H3, we could prevent the most damaging and most virulent cause of influenza each winter.”
