How Could Time Travelers Avoid Diseases?

When we go to another country, we often get recommendations for vaccinations that will protect us from diseases we don't worry about at home. It would be the same for time travelers, depending on what era of history they are going to. For example, I might be able to travel to a time where smallpox was rampant, but my children would not, since they never got the smallpox vaccine. In the 21st century, we don't worry about the plague or leprosy because they are treatable, but going to the past means you also go back to when we didn't have antibiotics, so you'd better take some. If you travel to the future, you may find yourself in the middle of a sigma flu epidemic, and you are the only one in town who hasn't had a sigma flu shot -because you've never heard of sigma flu. Hank Green gives us some perspective on that one aspect of time travel that science fiction writers never think of.