If a person was born and grew up in a country where HAV infection is endemic (e.g., Vietnam, Mexico) and then moved to the United States at age 20, should that person receive HepA vaccine before returning to visit his/her homeland?

It depends on whether that person has a history of HAV infection. Unless there are medical records that document prior HAV infection, serologic testing for immunity (positive test for total anti-HAV) is the only way to determine if vaccination is necessary. For people from countries with high rates of HAV infection, such as Vietnam and Mexico, serologic testing might be done to prevent unnecessary vaccination. The cost effectiveness of serologic testing, however, should be balanced against the possibility of delaying needed vaccination while awaiting test results.