No vaccine is 100% effective at preventing illness, but vaccines provide strong protection against serious illness, hospitalization, and death. You can still pass the disease on to another person after you’ve been vaccinated, which is why if you have symptoms of COVID or flu, you should consider staying home or think about wearing a mask that covers your nose and mouth if you must be around other people. It’s important to keep up to date on vaccines like COVID and flu, because they are updated every year to target new versions of each virus.