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Penn expert raises questions about this year’s flu shots but says to get one anyway

It looks like a bad flu season, he said, and the shots may keep you out of the hospital.

Acme pharmacist Dawn Cohen, gives Roberta Leiggi, 81, of Levittown, Pa., her COVID-19 booster shot and her flu shot at the Bristol Township Senior Center in Bristol, Pa., on Nov. 9, 2021. .
Acme pharmacist Dawn Cohen, gives Roberta Leiggi, 81, of Levittown, Pa., her COVID-19 booster shot and her flu shot at the Bristol Township Senior Center in Bristol, Pa., on Nov. 9, 2021. .Read moreTYGER WILLIAMS / Staff Photographer

Want some more bad virus news?

Scott Hensley, a viral immunologist at Penn Medicine, has some for you anyway. He and a team of researchers have been studying how well this year’s flu vaccines are likely to work.

Each year, a Food and Drug Administration committee tells vaccine manufacturers to produce shots aimed at four strains of flu virus that circulated during the past season. That was especially challenging this year, because precautions against COVID-19 kept the world from having much of a flu season. An FDA committee last March settled on versions of two type A flus — H1N1 and H3N2 — and two type Bs — Victoria and Yamagata lineage.

So far, H3N2 has been the dominant strain. It has spread quickly, starting first with children and young adults and then moving into older people. Unfortunately, Hensley said, it’s not quite the version of H3N2 that scientists expected months ago, and his team’s work in the laboratory showed the vaccine likely won’t be great at neutralizing infection with this different H3N2. The results were published in a preprint manuscript this week on

That doesn’t mean you shouldn’t get a shot, Hensley said. In fact, he strongly recommends getting one.

“By no means should our data be used as a rationale for not receiving the vaccine,” he said.

There are plenty of signs, he said, that this could be a rough flu season on top of a rough COVID-19 season, so do what you can to stay out of very busy hospitals. Flu vaccines may work well against other strains that might become more common later in the season. No one knows how long this particular H3N2 will stick around. “Flu is always throwing us surprises,” Hensley said.

Plus, he said, even when flu shots don’t keep you from getting sick, they do seem to prevent hospitalizations and deaths.

Hensley’s team did laboratory studies on the blood of 40 vaccinated people, most of them young adults. He said that it’s too early to know how the vaccines will perform outside of the lab but that these tests usually correlate well with real-world performance. During a large outbreak at the University of Michigan this fall, for example, vaccine protection was “low,” according to a report in the CDC’s Morbidity and Mortality Weekly Report.

H3N2 strains have long been challenging for vaccine producers, because they mutate quickly and do not grow well in chicken eggs, which are used to produce vaccine. The viruses tend to change slightly so they can reproduce faster in eggs, but that makes them different from the “wild-type” virus they are meant to thwart, Hensley said. That happened this year, so the vaccines were not even a good match for this year’s identified wild-type H3N2. Then it turned out that dominant version of H3N2 had important changes that were even harder for the vaccine to recognize.

Hensley found that the vaccine worked well against egg-adapted H3N2, less well against the wild-type H3N2 chosen for this year’s vaccine, and poorly against the H3N2 that’s now making people sick. Neutralizing antibodies were undetectable in 35% of samples for the wild-type H3N2 and in 55% of samples for the dominant version. Even when there were antibodies, they were at low levels.

Hensley said it’s not clear why flu vaccines that aren’t all that good at preventing illness still keep people out of the hospital or funeral home. It could be that parts of the immune system that are harder to measure stop the virus from doing severe damage.

Meanwhile, the CDC on Friday reported that flu activity is increasing, particularly in the eastern and central parts of the United States. It also said hospitalizations for flu are up. Earlier this week, both Pennsylvania and New Jersey said cases were rising as well. Pennsylvania characterized spread as high, while New Jersey said flu activity was moderate in most of the state. Philadelphia on Friday also reported an increase in positive flu tests.

Aside from vaccination, Hensley said that people can help by doing the things that kept flu at bay last year: Stay home when you’re sick. Wear a mask in public. Maintain social distancing. Wash your hands.