I totally cannot foresee violent reactions to the door-knockers, both from more than rough around the edges rednecks and folks in the hood. Presumably, most of the door-knockers will be women, which makes this all that more intelligent. "Hello, we're with the health department, just spreading the word about the importance of COVID vaccination. Have you been vaccinated..."
We're a year and a half into this. The people who still aren't vaccinated don't want to get vaccinated. They all know about the vaccinations. A person knocking on their doors will, at the least, annoy them, and at most anger them. Neither of those reactions will make them more likely to get vaccinated. This will inevitably give birth to new conspiracy theories that these people are being used to identify and tally who has not been vaccinated for the purposes of blacklisting them or persecuting them.