In the words of the researchers, who published their results in the CDC’s Morbidity and Mortality Weekly Report, the vaccine “did not reduce the risk for outpatient respiratory illness caused by influenza A(H3N2) viruses that have predominated so far this season.”

Flu vaccines, even in a good year, are far from perfect. The strains of influenza virus that infect humans are constantly evolving, meaning that scientists have to try to predict what these strains will look like during the next flu season so that they can match them to the strains included in the vaccine (the vaccine will usually include four strains at a time). This guessing game often results in a vaccine that’s around 50% to 60% effective, but sometimes, as is the case this year, the mismatch can get worse. It doesn’t help that this year’s main flu is H3N2, a subtype of flu already known for being harder to predict than others.

The lucky break this winter is that the flu has taken another hiatus. Cases, hospitalizations, and deaths are well under historical trends, though not as quite as low as they were during the 2020-2021 winter flu season.