Because there is a disease control center in Atlanta, if anyone in the United States can develop a vaccine against diseases, it is estimated that only scientists here are most likely. Moreover, in order to protect the institutions that develop vaccines, if the government still exists, it will definitely send heavy troops to protect this place, which will be much safer than other places.
Of course, this is only a theoretical situation, and there are many examples of the fall of the CDC in film and television works.