booster
n. countable B2 Upper Intermediate US //ˈbustɝ// UK //bˈuːstɐ// boost·er
n. an extra dose of medicine that strengthens your immunity. You get a booster when the protection from your first shots starts to fade.
n. an additional dose of a vaccine administered to maintain or increase immunity. Also used for any device or substance that enhances performance or support.
She got a booster shot last week.
The doctor recommended a booster to keep the vaccine protection strong.
The political campaign relied on a final media booster to sway undecided voters before the election.