CDC: Flu Vaccine Was Not Very Effective This Season

Woman getting a flu shot.

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Key Takeaways

  • The CDC reports that the flu vaccine was not very effective at preventing mild or moderate infections this season.
  • Experts still recommend getting the flu shot to prevent hospitalizations or death, especially in young children and immunocompromised people.
  • Masking, social distancing, hand washing, and staying home when sick are other ways to protect yourself against the flu.

The flu vaccine was not very effective at reducing influenza infections this season, according to recently released preliminary data from the Centers for Disease Control and Prevention (CDC).  

Based on a study of more than 3,600 children and adults in the United States from October 2021 to February 2022, the CDC reported that the vaccine was only around 16% effective against mild or moderate influenza infections, which is considered not statistically significant. Vaccines are typically 40% to 60% effective.

“This analysis indicates that influenza vaccination did not reduce the risk for outpatient medically attended illness with influenza A(H3N2) viruses that predominated so far this season,” the CDC report stated.

Despite a less effective vaccine, flu activity and cases remained relatively low this year. The CDC’s influenza tracker called shows that cases peaked during the last week of 2021 and have remained below the national baseline for the last five weeks.

Why Was the Flu Vaccine Less Effective This Season? 

Flu vaccines are typically developed based on the previous year’s flu season. However, if flu cases are low that season, it can make the following vaccine strain less effective, Purvi Parikh, MD, allergist and immunologist at NYU Langone Health, told Verywell in an email.

The predominant strain of influenza that is circulating this season is A (H3N2), but according to health experts, this year’s strain is a poor match to the vaccine strain, causing the vaccine to be less effective overall.

“We had a mild flu season last year so this gave the scientists determining the next vaccine fewer data on which to select the best array of influenza types,” Davidson Hamer, MD, professor of global health and medicine at Boston University School of Public Health, told Verywell in an email. 

We had another mild flu season this year presumably because of COVID-19 control measures—masking and social distancing—which have reduced transmission. This mean's there is a smaller number of cases on which to assess the vaccine’s effectiveness, Hamer said.

Why Are Flu Cases Low?

According to Parikh, in 2020 and 2021 more people got their flu shots compared to previous years. This factor combined with COVID-19 restrictions and other protocols—including masks, working from home, social distancing, and cancellations of events and gatherings—helps ensure cases stay low.

She added that restrictions and higher vaccination rates for influenza could have contributed to fewer flu cases last year as well.

William Schaffner, MD, professor of preventive medicine and health policy at Vanderbilt University Medical Center, told Verywell that children masking in schools may be helping keep cases low these past two years.

“Children are thought to be the great disseminators of the influenza virus in our communities. When children get infected with the virus, they shed more virus and they do so for a longer period of time than adults,” Schaffner said. “But because children were still largely masked, that contributed to an abbreviated influenza season this year.”

Despite low flu cases, influenza circulation has picked up and remains at high levels in multiple countries, Aubree Gordon, PhD, associate professor of epidemiology at the University of Michigan School of Public Health, told Verywell. This means communities may not be out of the woods yet.

What This Means For You

Even though flu vaccines were not as effective at preventing mild or moderate infection this season, health experts still recommend getting the flu shot next season. The best time to get vaccinated is between the end of September and the end of November.

You Should Still Get the Flu Shot

Even though the flu vaccine was not as effective at providing complete protection against the disease, health experts including Schaffner believe the vaccine is still the best way to prevent hospitalizations or death.

This is especially true for young children, immunocompromised people, patients with diabetes and underlying illness, and cancer patients.

“People who received the vaccine were less likely to need hospitalization, intensive care unit admission, and dying than comparable people who were unvaccinated,” he said. “Influenza vaccine prevents many illnesses and hospitalizations completely. It’s the best vaccine that we have available and can produce at the present time.”

However, since this year’s flu season is ending and spring is coming, Hamer no longer recommends you get the vaccine right now unless you are planning international travel to parts of the world, like the Southern Hemisphere, where there may be greater flu transmission.

The CDC says flu activity usually starts to rise in October and usually peaks between December and February, though there is often still plenty of flu in circulation in March.

“Starting at the end of September through October and before Thanksgiving, that’s the ideal time,” Schaffner said. “If you happen to forget, get it anyway because flu usually peaks in the United States in February. So the vaccines still have a chance to protect you.”

There are other things you can do beyond vaccination to protect yourself against the flu. This includes wearing a mask in high traffic areas, washing hands frequently, staying at home when sick, social distancing, and testing for flu when appropriate.

Despite these measures, experts believe the best way to prevent severe disease and infection is to get vaccinated.

“The flu shot is a life-saving intervention, we cannot really compare efficacy to other years given low cases overall,” Parikh said. “The fact that the vaccine is made based on the prior year which also had low cases does not mean the vaccine doesn’t work, it just means the wrong strain was predicted.”

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3 Sources
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  2. Centers for Disease Control and Prevention. Vaccine effectiveness: how well do flu vaccines work?

  3. Centers for Disease Control and Prevention. Flu season.