Measles seroprevalence among healthcare workers in South Korea during the post-elimination period.

During the measles epidemic in 2019, in-hospital transmission of measles contributed to more than two-thirds of measles cases in South Korea, where measles is declared eliminated. This study aimed to examine measles seropositivity among healthcare workers (HCWs) in South Korea to help develop an effective measles prevention strategy for hospital settings. Measles IgG titer was tested in 1,579 HCWs working in a university-affiliated hospital and the measles-containing vaccine (MCV) immunization records of 870 HCWs were identified. The overall seropositivity was 92.0%, but the seropositivity and antibody titers were significantly low among HCWs aged 20-25 years (78.6%) and among one-dose vaccine recipients (86.7%). Among two-dose recipients, seropositivity was lower among young HCWs who received two doses during their childhood than among those who received the catch-up vaccination as part of job requirements (70.3% vs. 98.0%). Among 87 seronegative HCWs who received two-dose MMR vaccination, the seroconversion rate was 98.9%. A considerable proportion of young HCWs were potentially susceptible to measles despite receiving the two-dose vaccination during childhood because of the waning immunity against measles in a country with measles-eliminated status. Serological screening for measles of newly employed HCWs and MCV immunization of seronegative HCWs appears to be an effective prevention strategy.