This year's flu shots are a 'very good match' to circulating strains, health officials say

This year's flu shots appear to be a "very good match" to the circulating influenza strains, health officials say. However, even though flu season got off to an unusually early start, vaccination rates, especially among adults, are lagging those seen this time last year. 

"I can tell you firsthand: This year's flu season is off to a rough start," Dr. Sandra Fryhofer, the board chair of the American Medical Association and an internist, told reporters during a news conference Monday (Dec. 5). "We've forgotten how bad the flu can be. But this year's season is a shout out that it can get really bad and it's here, so people need to get vaccinated."

According to the Centers for Disease Control and Prevention's (CDC) latest flu surveillance report, more than 19,500 patients with influenza were admitted to hospitals between Nov. 20 and Nov. 26, compared with roughly 11,200 people hospitalized the week prior. 

So far this season, 14 children have died of the flu, half of whom died between mid- and late-November.

Related: Which flu shot should I get?  

As of Nov. 19, about 154.1 million doses of flu vaccine had been administered in the U.S., the CDC reported. An estimated 40% of the country's children and adolescents ages 6 months to 17 years had gotten a flu shot as of that date — about the same fraction as had by the same date last season. However, adults seem to be lagging slightly: As of mid-November, 51.7 million doses had been given to adults, compared with 54.1 million by the same time last year, the CDC reported. 

Likewise, vaccination rates among vulnerable adults have been low compared with last season. For example, as of October, vaccinations among pregnant people were down 12% compared with the same time last year, and among people ages 65 and older, the rate was down about 3%, Dr. Rochelle Walensky, director of the CDC, told reporters Monday. These groups, children younger than 5, and people with heart disease, asthma, kidney disease and diabetes face the highest risk of complications and death from influenza.

It's not too late to get a flu vaccine, and real-time data suggest that this year's shots are protective against the circulating strains. "The good news is that it looks like it is a very good match," Walensky said.

This year's flu shots protect against four types of flu viruses: two influenza A and two influenza B viruses. According to data collected by public health laboratories, more than 99% of the circulating viruses are influenza A, with most being A(H3N2) and a minority being A(H1N1). So far, the strains circulating look similar to the ones included in the vaccine, which means the shots should effectively train the immune system to recognize the viruses, the CDC surveillance report states.

Because different flu strains could gain prominence later in the season, we won't know exactly how protective this season's shots are until early 2023, but in general, flu shots have historically been about 40% to 60% effective when they're a "good match." In this context, that means vaccinated individuals would be 40% to 60% less likely to visit the doctor for flu than people who aren't vaccinated. And although flu shots don't completely eliminate your chance of falling ill, when vaccinated individuals catch the flu, they have a lower chance of severe illness and death than unvaccinated people. 

You should still get a flu shot even if you've already caught influenza this season, because the shots may protect you against a different strain than the one you got. 

"The only thing worse than getting flu once in a season is getting it again" after being exposed to a different strain, Fryhofer said.