A Serosurvey Identifying Vulnerability to Measles in Health Care Workers. A Hospital-Based Prospective Seroprevalence Study.

The aim of this serological survey was to assess the persistence of measles antibodies among health care workers (HCWs) at risk of incidental measles. A prospective study of measles-specific antibodies in serum samples obtained from a total of 2782 participants aged 19-89 years was conducted between May 2018 and December 2019. The seropositivity rate of 93.7% (95% CI: 92.4-94.9%) in fully vaccinated participants aged 19-48 years was significantly lower than that of 98.0% (95% CI: 96.5-99.0%) in participants naturally immunised before 54 years. A cohort of those born in 1971-1975, vaccinated predominantly with one dose, showed lower seropositivity persistence (86.6%) than those fully vaccinated with two doses or naturally immunised. Otherwise, seropositivity was not markedly influenced by sex, age, smoking status, overweight, obesity or concomitant disease. The presence of sufficient antibody levels in a high proportion of HCWs irrespective of the way they acquired immunity is a favourable finding for managing incidental measles; hence, in the presence of a risk of a measles outbreak, it would be possible to perform targeted vaccination of only at-risk HCWs with a history of incomplete vaccination or missing information about the way in which immunity is acquired.