vac ‧ cine /ˈvæksiːn $ vækˈsiːn/ BrE AmE noun [uncountable and countable]
[ Date: 1700-1800 ; Language: Latin ; Origin: vaccinus 'of a cow' , from vacca 'cow' ; because the substance was originally obtained from sick cows ]
a substance which contains a weak form of the ↑ bacteria or ↑ virus that causes a disease and is used to protect people from that disease:
a polio vaccine
Doctors worried that there would not be enough vaccine for everyone who needed it.