People getting a flu shot this year will receive three vaccines instead of the more common four, because one species went extinct during the pandemic. Mark J. Terrill/AP Hide Caption
Toggle caption Mark J. Terrill/AP
This year's flu shot will no longer contain the strains of influenza that have been protected against for more than a decade.
This is because no cases of influenza B/Yamagata strain influenza have been confirmed since spring 2020. And the Food and Drug Administration determined this year that the strain currently poses little or no threat to human health.
Scientists concluded that physical distancing and mask-wearing, which were widely practiced in the early days of the coronavirus outbreak, likely pushed B/Yamagata into oblivion.
Dr. Rebecca Wurz, an infectious disease physician and epidemiologist at the University of Minnesota School of Public Health, said this surprised many who study influenza because this is the first time on record that a virus has been wiped out by a change in human behavior. This is because it is the first time such a case has been reported, he said.
“This is a very interesting and unique story,” Wurtz said, adding that B/Yamagata would still be widespread if it weren't for the coronavirus.
One reason COVID-19 mitigation efforts have been so effective in eliminating type B/Yamagata is that a significant amount of immunity to this strain of influenza already exists in the population, and was circulating at low levels, said Dr. Kausar Talat, an infectious disease physician. at the Johns Hopkins University Bloomberg School of Public Health.
In contrast, SARS-CoV-2 was an entirely new virus that no one had ever encountered before. Therefore, masking and isolation can only slow, not stop, the transmission of infection.
B/Yamagata's absence will not change the experience of getting this year's flu shot, which the Centers for Disease Control and Prevention recommends for everyone 6 months and older. Unvaccinated people are also less likely to get the flu, as influenza B/Victoria and the two influenza A strains are still widely circulating and making people sick. Talaat said the disappearance of B/Yamagata does not appear to have reduced the overall burden of influenza, noting that the level of illness caused by any strain varies from year to year.
The CDC estimates that between 12,000 and 51,000 people die from influenza each year.
However, the manufacturing process has been simplified because the vaccine is now a trivalent vaccine (designed to protect against three types of influenza viruses) rather than a quadrivalent vaccine that protects against four types of influenza viruses. The change will allow the company to produce more doses, Talaat said.
Ultimately, Talaat said, the costs of continuing to include protection against B/Cyrus in influenza vaccinations outweigh the benefits.
“If you put a strain into a vaccine that you don't think will infect anyone, there are potential risks but no potential benefits,” he said. “Even if the risk is minimal, the benefit is also minimal.”
Kevin R. McCarthy, an assistant professor at the University of Pittsburgh's Vaccine Research Center, said scientists and public health experts have spent the past few years wondering whether to exclude influenza B/Yamagata from influenza vaccines or wait for a possible resurgence. They have been debating whether it should be done. However, Mr McCarthy agrees that continuing to vaccinate against B/salt beetles does not benefit public health.
Additionally, there is a small chance that B/Yamagata could inadvertently infect workers manufacturing influenza vaccines. The virus that grows in the eggs is inactivated before vaccination. You cannot get the flu from getting the flu shot. However, exposure of workers to live B/Champion may occur before it becomes harmless.
If B/Yamagata no longer makes people sick, it could lead to the reintroduction of the virus to people with weakened immunity. The risk is very low, but it doesn't make sense to produce thousands of gallons of a virus that is likely extinct, McCarthy said.
B/Champion may continue to be present in some parts of the world where comprehensive influenza surveillance is inadequate. But humans are the only host population for influenza B viruses, so scientists aren't worried that the virus is hiding in animals.
Scientists have determined that the B/wild moth disappeared in a relatively short period of time, which in itself is a success, McCarthy said. That required cooperation and data sharing from people around the world, including countries with weak diplomatic relations with the United States such as China and Russia.
“I think the fact that we can do that shows we can do some things right,” he said.
Sarah Borden is an independent health science journalist based in Pittsburgh.
