The Flu Vaccine This Year Was Basically Worthless

What is a flu vaccine?

Influenza vaccines, usually known as flu jabs or flu shots, are antiviral vaccines that protect against influenza virus infection.

As the influenza virus evolves rapidly, new vaccine versions are generated twice a year.

While their effectiveness varies from year to year, the majority provide moderate to high influenza protection.

The Centers for Disease Control and Prevention (CDC) in the United States estimates that influenza vaccine reduces illness, medical visits, hospitalizations, and fatalities.

According to a new analysis from the Centers for Disease Control and Prevention, this winter's flu vaccine was a very poor match for the most common influenza strain in circulation. For the second year in a succession, the flu season was much milder than typical, thanks to continued covid-19 measures, which presumably slowed the spread of flu as well.

The figures are based on the CDC's long-running surveillance program of people who visit various outpatient sites across the country with suspected flu-like symptoms. The researchers discovered that vaccinated patients had only a modestly decreased chance of contracting a confirmed case of flu. The vaccination was found to be 14 percent effective against all flu strains reported at these locations, as well as 16 percent effective at preventing instances of flu from A(H3N2) viruses, the most common strain this winter. These figures are well below the 50% criterion that a vaccination must meet to be regarded "relatively helpful," and they're not even close to statistical significance.

The vaccine "did not diminish the risk for outpatient respiratory illness caused by influenza A(H3N2) viruses that have predominated so far this season," according to the researchers, who published their findings in the CDC's Morbidity and Mortality Weekly Report.

Even in a good year, flu shots are far from flawless. Because human influenza virus strains are constantly developing, scientists must try to forecast what these strains will look like during the next flu season so that they may be matched to the strains in the vaccine (the vaccine will usually include four strains at a time). This guessing game usually yields a vaccination that is 50 percent to 60 percent effective, but the mismatch can sometimes worsen, as it has this year. It doesn't help that the primary flu this year is H3N2, a strain of flu that is already notorious for being more difficult to anticipate than others.

The flu has taken another respite this winter, which is a fortunate break. Cases, hospitalizations, and deaths are all considerably below historical levels, though not as low as they were during the winter flu season of 2020-2021. (At the time, the figures were so low that the CDC couldn't even assess vaccine effectiveness for that season.) The few instances seen the previous flu season made forecasting this year's flu season much more difficult. The mildness of the past two flu seasons has been attributed to public health efforts aimed at slowing the spread of the considerably more contagious SARS-CoV-2 virus, such as the wearing of masks on a regular basis.

Last month, the World Health Organization released its recommendations for flu vaccines for the Northern Hemisphere's winter season, which included a request for revisions to the H3N2 strains used as a reference. "Predicting the circulation of viral subtypes and prominent clades among subtypes remains problematic," the CDC experts write.

However, just because this year's flu vaccine was a flop doesn't mean they're not worth getting. Despite the fact that only about half of all Americans are vaccinated, flu shots are expected to prevent millions of flu infections, tens of thousands of hospitalizations, and at least thousands of fatalities in a typical year. Next-generation flu vaccinations are also in the works, which could allow for a better match to circulating strains. Furthermore, the allure of a universal or longer-lasting flu vaccine remains tantalizingly close.

Even in the absence of very efficient vaccines, the past two winters should serve as a reminder that bad flu seasons do not have to be unavoidable.