NEW YORK — The flu vaccine did a disappointing job last winter in the U.S., and officials worry that might be a bad sign for the fall.

Flu vaccines had been about 60 percent effective against the type of flu that caused the most lab-confirmed illnesses last winter, but last season’s vaccine was only about half that good, according to study results reported Wednesday.

Against another major type of flu, vaccines have already been only around 30 percent effective.

The new results may be a sign of shrinking effectiveness against a number of strains, and “that’s concerning,” said Brendan Flannery, who oversees the U.S. Centers for Disease Control and Prevention’s system for evaluating the vaccine.

The results come as health officials are gearing up for a critically important flu vaccination campaign, with a record 180 million doses being prepared. U.S. health officials fear a second wave of coronavirus infections, and reducing flu illnesses could help reduce patient traffic if COVID-19 causes doctors’ offices and hospitals to become overwhelmed.