Incredible Torah Temimah to share with you. Thousands of years ago our sages knew more about how to react in times of plagues and viruses than most of the "experts" of today, with all their technology and presumed enlightenment. Don't try this at home, kids, but those who are true masters of the Torah can derive all knowledge of this world from the Torah. The translation is my own.

Torah Temima on the Torah, Sh'mos 12:22

"And you shall not go out". The Rabbis taught, when a plague is in the city, gather in your feet [stay inside], as it says "And you shall not go out, a man from the entrance of his home until the morning." (Bava Kama 60B)

We normally explain "gather in your feet" to mean that one should not flee his city to another city, and in contrast to what is written here [it says] when a famine is in the city, scatter your feet. There it means that one should leave the city, as it brings the proof there from the verse "And there was a famine in the land, and Avram went down to Egypt."

However, the Maharsha writes that regarding a plague we cannot explain it thus, for certainly when a plague is in the city it is also good to scatter one's feet, meaning to escape for one's life. Rather, here is means that so long as one does not leave the city, he should gather his feet to his home and not go out in the streets. These are his words.

It is unclear how he knows to explain it like this based only on logic. Indeed, also in the responsa of the Maharil (35) he writes similarly in a different vein. That is that in the beginning of the plague one should leave the city, but not in the end, and it is unclear how he knows this as well.

However, the words of the Maharsha are implied by the verse that the Gemara brings as well as support for this, and that is the verse in Yeshaya 26, which is referring there to the time during the plague: “Go, my nation, come inside your rooms and your doors for your sake...until the anger will pass.” This implies that “gathering in” refers to inside the home. And also from that which they bring there, from the verse in Parshas Ha'azinu, “Outside the sword will bereave, and inside there will be fright,” implies that if they are simply not outside they will have a small rescue.

As for what the Maharsha writes based on logic that when there is a plague in the city it is good to escape for one's life – the truth is that one can bring a proof to this from Taanis 20B. They said to Shmuel, there is a plague in Bei Chozai. He decreed a fast in his city, and the reason is explained that because there were caravans [going from Bei Chozai to Neharda'ah] it would come with them. That being the case, all the more so in the city [of Bei Chozai] itself it would be possible for the illness to be contracted.

And this is like what Rabbeinu Bachye writes in Parshas Korach a reason for what Hashem writes, “Separate from this congregation and I will consume them,” it is so that they should not be infected by the bad air of the plague, as it says by the wife of Lot, “And she looked behind him...”

As for what the Maharil writes that at the end of the plague one should not leave the city, perhaps the reason is that since it has already become entrenched in the city and has not harmed him, he has already become used to it [immune] and it will no longer harm him.

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In sum, he reconciles seemingly conflicting sources to suggest that before a plague has become widespread in an area, it is advisable to leave the area. However, once the plague is widespread, it is best to remain indoors until it passes. Once this occurs, it is best NOT to leave the city, for he is likely immune to the strain that afflicted the city. Gold.