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  • The CDC posted early research finding the flu shot was about 54% effective for people under 65. It was even more effective for children and teens.
  • This flu season started early and has resulted in around 25 million illnesses.
  • The number of people who got the flu vaccine was slightly lower than average at about 49%

During the COVID-19 pandemic, seasonal flu cases were lower than average. But this year cases roared back with a high number of cases early in the season.

According to the Centers for Disease Prevention and Control (CDC), there were an estimated 25 million illnesses, 280,000 hospitalizations, and 18,000 flu-related deaths caused by this flu season as of February 24, 2023.

Now new research finds that the seasonal flu shot was about 54% effective at protecting adults people under 65 against disease. The seasonal flu shot is usually about 40 to 60% effective at preventing disease.

So was this year’s flu season as bad as previous years? Healthline spoke with public health experts to get their take.

According to the Centers for Disease Control and Prevention (CDC), studies have shown that “flu vaccination reduces the risk of flu illness by between 40% and 60% among the overall population during seasons when most circulating flu viruses are well-matched to those used to make flu vaccines.”

There are ways to determine flu vaccines’ efficacy and effectiveness. While efficacy is determined by using randomized trials, usually in a clinical setting, this methodology doesn’t tell how effective the flu vaccine is in real-world conditions.

“The flu vaccine effectiveness estimates are pretty approximate because we don’t do clinical trials that are randomized like we did for the COVID vaccine, “ says Andrew Noymer, PhD, Associate Professor, Population Health and Disease Prevention, University of California, Irvine– Program in Public Health, “They do case-control studies after the fact.”

The CDC released an interim report based on data from a Wisconsin sample.

Data from this report found the effectiveness of the 2022–23 influenza vaccine found it provided 54% protection in preventing serious illness in people under 65 years and 71% protection in preventing symptomatic influenza A illness among children and adolescents younger than 18 years.

“A lot of people getting sick could be considered a severe season, but we could also have seasons with lower case rates but higher rates of serious disease and death that would be considered severe,” shared Brian Labus, PhD, MPH, REHS, Assistant Professor, Department of Epidemiology and Biostatistics, School of Public Health, University of Nevada, Las Vegas, “Not everyone experiences flu season the same way.”

If more people get the flu shot, is the flu season going to be less severe?

“That’s the topic of some debate and ongoing research,” said Noymer, “In general, it’s a partial correlation at best.”

Noymer said that the flu vaccine in some seasons is more effective at preventing disease and that the severity of the flu season is not governed entirely by how many flu shots people get.

Labus shares that the vaccine could be a complete mismatch for the circulating strain or it could be a great match, which can account for a lot more variability.

In general, the flu vaccine often offers better protection against specific strains: influenza A and B(H1N1) viruses. It generally offers less protection against influenza A(H3N2). Additionally, it matters whether or not the current vaccine is a‘good match’ for the circulating strain meaning it’s targeting the strain that is spreading widely.

“(Vaccine) strain match is more important than vaccine uptake simply because of the math,” advised Labus. The US influenza vaccination rates are fairly stable, with around 55% of the population getting vaccinated each year.

The FDA is meeting next week to select next year’s vaccine strains to give manufacturers time to produce the vaccine for the fall. Labus cautions that sometimes new strains emerge and the predictions made that far in advance are incorrect.

This year the vaccination rates were a little lower than the year prior at about 47.9% for this flu season compared to 55.6% for the year prior.

Flu vaccination rates for persons over 18 years for 2021-22 season was 49%.

The lower vaccination rate did not surprise Labus.

“It’s not surprising given that we saw a very early flu season this winter. Flu activity usually peaks in late February but this year it peaked around Thanksgiving and was mostly over by early January,” says Labus. “It’s hard to convince people of the benefit of the flu shot if the season is basically in the rear view mirror.”

Officially, the “severity” of this year’s flu season and the impact of the flu vaccine has not been determined. The CDC does a post-mortem report on the flu season to try to estimate flu vaccine efficacy, but since it’s still February, the flu season isn’t officially over yet.

“This year’s flu season has actually been pretty typical in terms of severity,” says Labus. “The big difference has been in the timing of the season.”

The season peaked around Thanksgiving, and there was a lot of attention given to the big increase in RSV cases seen in children rather than flu, so people may have just perceived the flu season a bit differently.

The 2022-23 flu season is relatively on par with previous years. The main difference has been that the 2022-23 season peaked earlier and was also confounded with increased cases of RSV. Regardless, medical experts agree that the best way to protect yourself and loved ones against the flu is to get vaccinated.

Early reports find that the flu vaccine was 54% effective for adults under the age of 65 and 71% effective at providing protection for children and adolescents under the age of 18.