Noun
immunity to a particular disease that is not innate but has been acquired during life; immunity can be acquired by the development of antibodies after an attack of an infectious disease or by a pregnant mother passing antibodies through the placenta to a fetus or by vaccination
Source: WordNetAn acquired immunity or introduced immunity – vaccine – can give that advantage. Source: Internet
“COVID-19 is a ‘new’ virus, so there is no acquired immunity, and is more severe in the elderly who have a weaker immune system, and often intercurrent heart or lung problems, among others. Source: Internet