booster
boost-er
noun
An additional dose of a vaccine to strengthen or prolong immunity.
"She received her COVID-19 booster jab last week."
noun
A device or substance that increases power, force, or effectiveness.
"The signal booster improved the Wi-Fi connection."
Thesaurus
Synonyms: admirer, protagonist, champion, friend, supporter, plugger, promoter, relay link, relay station, booster station, booster amplifier, relay transmitter