This year’s flu vaccine is a “major mismatch,” meaning it may not prevent against infection. But experts say people should still get the shot because it will keep severe disease at bay. CNN reports that the main strain of the flu virus that’s circulating has mutated and the vaccine prepped well before flu season does not appear to create antibodies against the variations. But the good news is that the mutations don’t affect another part of the immune system—T-cells—and those can stop you from getting very, very sick if you catch the flu. The mismatch has happened before, and people who were vaccinated fared better than those who skipped the shot.