Someone sent the question to the posek Rav Yehuda Aryeh Dinner in Bnei Braq asking what to do to prevent getting infected with the CoronaVirus.

Somehow I doubt he was asking for medical advice such as which vitamins to take or which medicines can be used preventatively (such as some people saying take vitamin D and zinc or Hydroxychloroquine) and was more likely asking from a spiritual perspective, such as stop talking lashon hara or do more chessed, be more careful about tzniyus or whatever.

Rav Dinner responded with the following instructions:

1. rub apple cider vinegar on your nostril three times a day - in the morning, afternoon and before going to sleep

2. mix apple cider vinegar with water and drink it three times a day

3. somebody who is already sick with Corona should do the same but double the dosage

Rav Dinner then closes his comments referencing a rabbi in Montreal who made the claim that nobody who did this got sick at all.

sources: Kikar, Hamechadesh

I would just note that there are many articles that say the apple cider vinegar treatment does nothing to prevent or heal CoronaVirus.