Yes, you can still get the flu after a flu shot.
Getting a flu shot often protects you from coming down with the flu. And although the flu shot doesn't always provide total protection, it's worth getting.
The flu vaccine is not 100% effective
The flu vaccine is not 100% effective, so there's still a chance you can get the flu even after you've been vaccinated.
That's because scientists don't always correctly match the viruses in the vaccine with those that pop up during the flu season. This is what's called a mismatch.
A weakened immune system increases your risk
If you have a weakened or impaired immune system, it increases your chances of getting the flu, even if you've been vaccinated. This includes infants, children, and the elderly. That's because the flu vaccine works by triggering your immune system.
After you receive the flu vaccine, the viral strains come into contact with your body's B cells, a special type of cell whose job is to recognize foreign invaders and prepare your body to fight them. So when your B cells spot a full-strength virus, they produce antibodies that attach themselves to the virus and, eventually, another type of immune system cell called phagocytes overwhelm and destroy the virus.
The flu vaccine doesn't work immediately
After getting your flu vaccine, it can take the average healthy adult's immune system up to two weeks to build up enough antibodies for protection.
Getting the flu shot is your best chance at protection against the flu, even in years where scientists don't get it completely right. Your best bet is to also make sure to practice proper hand hygiene and respiratory etiquette — like using tissues and coughing or sneezing into your elbow instead of your hands — to improve your chances of avoiding the flu.