A flu variant vanishes

Opinion

Hey there, time traveller!
This article was published 16/03/2024 (572 days ago), so information in it may no longer be current.

For years, influenza shots have been immunizing people to protect them from an illness that can kill — 290,000 to 650,000 people die from influenza every year.

Recently, the vaccines have been quadrivalent, meaning they protect against four flu strains — two influenza A strains, A(H1N1)pdm09 and A(H3N2), and two influenza B strains, one from the B/Victoria/2/87 lineage, and the other from the B/Yamagata/16/88 line.

Next year, the Centers for Disease Control (CDC) in the United States will move to a trivalent vaccine — because one strain of flu, the influenza B Yamagata strain, has disappeared.

And the prevailing theory is that COVID-19 is to blame. Well, yes, but no.

Stay with us here.

Yamagata was already a flu variant in decline in 2020. But then along came COVID, and with it, masking mandates and controls on public gatherings.

Now, epidemiologists can’t find B-Yamagata anywhere. And they’ve looked. Scientists tested 15,878 samples from people who had influenza B in 2023 and were unable to find even a single case of B-Yamagata.

As a research article in the scientific journal viruses put it in 2022, “However, the pandemic caused by the SARS-CoV-2 virus, and the imposed public health countermeasures, have resulted in some unexpected consequences. The Yamagata lineage of influenza B viruses has not been isolated since March of 2020 … this is most likely resulting from the restrictions on travel and gatherings, as well as widespread mask use, since these limited the spreading of not only SARS-CoV-2, but also the various influenza strains.”

Oh, and B-Yamagata wasn’t the only influenza affected by masking: as Canada’s National Advisory Panel on Immunization has pointed out, “Global influenza circulation was at a historical low during the 2020-2021 influenza season, when public health measures (e.g., masking, social distancing) effectively suppressed seasonal influenza activity.”

Sadly, when masks came off, influenza came back to normal levels. Except for B-Yamagata — it was already the weakest link in the four common influenzas. Its transmission rate was lower, as was its ability to mutate.

Last September, the World Health Organization recommended that influenza vaccinations stop including protections to block B-Yamagata. And in early March, the U.S. Food and Drug administration made it official, saying vaccines for the 2024-25 flu season will be trivalent formulations. B-Yamagata is off the list. Canada hasn’t announced its plans yet — they often come as late as May — but look for the same thing to happen here.

Simplifying the vaccine could increase vaccine production, meaning more doses could be available in the developing world to help control the three remaining influenza variants.

It’s interesting to think that masking and reduced personal contact did what an effective vaccine could not — but key to the discussion is that vaccination rates for influenza in developed countries like the United States hover around 51 per cent of the population, meaning the virus still has half the population as, shall we say, a target market. And it’s not really a surprise that masking would work to stop infection — operating room teams have been wearing masks to reduce infections in patients, after all, since 1897.

As an object lesson in the effectiveness of masking and personal distancing if you’re sick, the B-Yamagata story probably won’t change any fully entrenched minds. But it should.

As a who-done-it, it’s a fascinating tale.

It’s also one worth thinking about as highly infectious measles makes its return from its own near-extinction story — thanks to people forgoing a highly-effective vaccine.

And what’s the No. 1 thing hospitals are told to do when a patient is suspected of having measles? Most advice looks like this, from the CDC: “Persons with signs or symptoms of measles should be identified, provided a facemask to wear, and separated from other patients.”

Fancy that.

Sometimes, it takes all the tools.