Crimes require “mens rea” (kavanah). “Innocent until proven guilty” is well rooted in common law and applies to all criminal matters. They could make it a crime to deliberately infect someone, which would cover deliberately getting an infection (though criminal statutes against self-harm are dubious, note that if someone commits suicide they are no longer hung up on a gallows).
To end the pandemic, only count someone as having Covid19 if they have symptoms more serious than flu or a cold or allergies (they did this when testing the vaccine). The number of positive cases would become very small since 90% of cases don’t result in illness. Announce the vaccine works (in tests, the placebo was 99% effective, the real vaccine was 99.9% effective), and allow everything to reopen. Seriously encourage old and sickly people to stay home, and wear N95 masks if they venture outside. In other words, declare victory and get back to normal.