PPIB and hepatitis B virus infection: Similar to hepatitis A vaccination, overall hepatitis B vaccination among travelers and persons with chronic liver disease has remained low, although hepatitis B vaccination of persons who had traveled outside the United States to a country in which hepatitis B is of high or intermediate endemicity was higher in 2015 and preceding years than among respondents who did not travel outside the United States or had traveled only to countries in which the disease is of low endemicity.