With the fast of 17 Tammuz fast approaching, in the middle of a pandemic, it raises the question of whether someone with CoronaVirus should fast or not on this upcoming fast day.

I have seen a number of piskei halacha announcements on this and they all seem pretty similar.

Chief Rabbi Rav Dovid Lau paskened that anyone sick with CoronaVirus or if one has symptoms of CoronaVirus (cough, difficulty breathing, weakness, etc), that person should not fast. If one has a temperature above 38C (100F) should not fast. Anyone eating because of CoronaVirus (even if he only suspects that he has it) should eat regularly and not bshiurim. Someone in isolation who feels fine, must fast.
source: Hamechadesh


Rav Yitzchak Zilbershtein paskened that anybody who has the CoronaVirus must eat on 17 Tammus. If someone is in isolation and thinks they might have cntracted the CoronaVirus, that person should eat "bshiurim" - in measured amounts of food less than a kzayit. If someone who suspects he might have Corona and is in isolation wants to fast anyway, he can only do so if he feels perfectly fine.
This goes for the upcoming Tisha B'Av fast as well.
source: Hamechadesh

Rav Moshe Bransdorfer paskened that one who has CoronaVirus or had it but still has weakness from it,  need not fast and if possible should make up the fast day later. Any other person should fast and not go out on the day, and if one must go out he should wear a mask. This is not like the fast of Erev Pesach that everyone was given a blanket psak to not fast - that was at the height of the pandemic and danger and now it is not at its full strength.

Rav Yosef Yitzchak Feigelstock, a Chabad rabbi in Buenos Aires, Argentina, paskened that anywhere that might still have CoronaVirus concerns, people should not fast on 17 Tammuz and 9 Av.

Anywhere there are sick people today, there is still danger. Because the doctors say that fasting makes one more prone to catching CoronaVirus, as the fasting weakens the body and the immune system, people in such places should not fast but should eat normally, without worrying about keeping the measurements down under the "shiurim" rule.

Someone who wants to fast anyway and is completely healthy - better to fast than to go to shul, so he should stay home all day..
source: Haredim10