(If a person gets both the flue and one or two Covid variants at thew same time, they may die.)

t's bad news for the vaccine, he said. Influenza vaccines protect against four different strains of the flu: H3N2, H1N1 and two strains of influenza B. Hensley's study only covers H3N2, but that happens to be the main circulating strain.

The vaccine mismatch may help explain an outbreak of flu at the University of Michigan last month that affected more than 700 people. More than 26% of those who tested positive had been vaccinated against flu -- the same percentage as those who tested negative. That indicates the vaccine was not effective in preventing infection.