Why Doesn't the Flu Vaccine Always Work?


Every year, we're reminded to get the flu vaccine. Many of us do. But each flu season, some vaccinated people still get the flu. Why? Shouldn't the vaccine protect us? Let's take a moment to learn why the flu vaccine doesn't always work.

Targeting the wrong viruses

One problem is that sometimes the flu vaccine doesn't target the right flu virus. Flu outbreaks can be caused by several different flu viruses. We don't know for sure which ones will be active in any given year. Researchers try to make predictions. Then, before each flu season, a vaccine is made to combat the most likely viruses. But the predictions aren't always right. Some years, the vaccine targets the wrong viruses.

Your personal history

Another reason the vaccine may not work is linked to your own history with the flu. Your immune system responds most strongly to viruses you've had in the past. You've built up antibodies to those viruses. But in a particular year, the flu may be caused by a virus you've never encountered. In that case, even if you've had the flu vaccine, your immune response may not be strong enough to fight off an infection.


Even though it isn't always 100 percent effective, most people should get the flu shot every year. The flu can be deadly, and getting the vaccine can save your life. Ask your doctor if the flu vaccine is right for you.