Flu Shots Have Been Working Well This Season, Data Suggest

The influenza vaccine has worked fairly well this season, preventing serious flu cases and hospitalizations across age groups, according to preliminary data released by the U.S. Centers for Disease Control and Prevention (CDC).

Flu shot efficacy varies from year to year, since different strains of the virus circulate each flu season. Experts do their best to tailor the shots to the strains expected to spread, but it’s not always a perfect fit. In some years, flu shot efficacy doesn’t break 30%.

So far, however, this season’s flu shots have been 71% effective at preventing symptomatic illness among children and 54% effective at preventing cases resulting in medical care among people younger than 65, according to a CDC report published Feb. 23 and based on data from Wisconsin. While those data are state-specific and based on a fairly small patient sample, the report notes that influenza strains circulating in Wisconsin tracked with those seen nationally.

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The numbers also align with several preliminary national estimates released by the CDC on Feb. 22. Those data—drawn from three different flu-monitoring networks, which include research sites across the country—suggest this season’s shots have been roughly 50% and 70% effective at preventing influenza-related hospitalizations among adults younger than 65 and kids, respectively. Protection has been a bit lower among older adults and people who are immunocompromised, but still around 40% by some of the estimates.

The current influenza season started early, with cases beginning to tick up in October and peaking in December. According to the CDC, this season’s circulating strains were a good match for those included in the annual flu shot, contributing to relatively high vaccine efficacy.

As with COVID-19 vaccines, flu shots don’t entirely prevent people from getting sick with influenza. But, compared to those who are unvaccinated, vaccinated people who get infected typically experience milder symptoms and have lower risks of developing cases that require medical care or hospitalization—which is why public-health officials recommend annual flu shots for almost everyone in the U.S., regardless of exactly how well that season’s shot goes on to work.