Measles immunity in medical center staff after changes in national and local hospital vaccination policies

BACKGROUND: Measles vaccination was introduced in Taiwan in 1978, and the disease was declared eliminated in Taiwan in 2007. However, new cases have been reported unpredictably since then. Hospital medical staff are at particularly high risk for measles. We evaluated the immunity status of hospital medical staff after changes in national and local hospital vaccination policies. METHODS: This retrospective study was conducted in a tertiary care medical center from January 2008 to June 2018. Data were retrieved from all healthcare workers receiving employment medical examinations. Those with a full medical record including the geometrical mean titer (GMT) of anti-measles IgG were included. Age and sex differences in the GMT were analyzed by Student’s t-tests and Chi-squared tests. Univariate and multivariate logistic regression analysis were used to determine the odds of immunity. RESULTS: The IgG positive rate increased with age group (p < 0.001). Seropositive rates for the birth before 1977 and after 1978 groups were 94.8% and 70.2% (p < 0.001). The odds ratio was also significantly different between both cohorts (1.000 vs. 0.423, p = 0.002). Staff in the examination department showed the lowest positive percentage of 70.3% (95% CI: 66.9–73.7%), whereas staff in preventive and long-term care services disclosed the highest positive percentage of 83.2% (95% CI: 76.1–90.2%). Subgroups 2015, 2017, and 2018 (p = 0.046, 0.046, 0.049), after the vaccination booster policy was launched, showed significant increases in seropositivity. CONCLUSIONS: Immunity efficacy is better in birth groups before 1977, which was highly related to natural infection before national policy launched. The policy of vaccination is an effective method, but medical staff attains inadequate protective antibody levels for maintenance of herd immunity. A pre-employment policy of screening a third booster vaccine of measles (or MMR) is recommended to lower the incidence of disease spreading and avoid outbreaks.