09-21-2021, 10:39 PM
If you know you've received killed vaccine but not two doses of the live type, you need another valid dose. If you can't find documentation that you received the series, are at higher risk, and it's been several decades since vaccination then it's probably best to just get revaccinated; another dose is astronomically unlikely to hurt you unless you're in the contraindicated group—pregnant, immunocompromised, or previously anaphylactic. This is not to be construed as health advice, but, there's even some limited evidence that recent MMR vaccination might provide some protection against severe COVID, due to immune cells it stimulates.