The coronavirus (COVID-19) vaccine should be referred to with the acronym as “COVID-19 vaccine”.
When discussing the COVID-19 vaccines in general, use “a COVID-19 vaccine” rather than “the COVID-19 vaccine”. This is because there are multiple types of vaccines and so we need to make it clear we are talking about all vaccines in general.
Only refer to a specific type of COVID-19 vaccine by name if you need to make the distinction between the vaccine types clear. There are currently three main COVID-19 vaccines: