Assessment of humoral immunity to the measles virus in healthcare workers

Background: Measles is a highly contagious, anthroponotic viral disease. In Russia, measles outbreaks were recorded in 2003, 2014, and 2019, with a rise in incidence noted since 2022. Catch-up vaccination of at-risk groups and revaccination of individuals previously vaccinated with a single dose continue. Determining antibody levels in the serum of vaccinated individuals and those with unknown vaccination and post-infection history remains relevant.

Aim: To present the results of a study on humoral immunity to the measles virus among healthcare workers, including those vaccinated against measles and individuals with unknown vaccination and post-infection history.

Materials and methods: An observational, single-center, cross-sectional, uncontrolled study was conducted. Inclusion criteria: employment in a healthcare organization; age over 18 years; documented history of vaccination and revaccination with a live measles vaccine completed at least three weeks before blood sampling, or unknown vaccination and post-infection status; absence of infectious disease symptoms at the time of blood sampling. The study was conducted over one month in 2024. Venous blood samples were collected, and measles virus-specific IgG antibodies (IU/ml) were determined in the serum using an enzyme-linked immunosorbent assay kit Vector-Best (Novosibirsk, Russia). The quantitative level of class G (IgG) antibodies to the measles virus was assessed. Statistical analysis was performed using StatTech v.4.1.9 software (developed by Stattech LLC, Russia).

Results: The median age of vaccinated participants (n=133) was 48 years (Q1–Q3: 41–54, max 76). In 66% of cases (88/133), antibody titers were at a protective level, with a mean antibody titer of 0.62 IU/ml (Q1–Q3: 0.07–2.52, max 5.0 IU/ml). During the evaluation of the relationship between antibody titers and the time since revaccination at the time of titer measurement, an inverse, weak correlation was observed. The mean age of individuals with unknown vaccination and post-infection history (n=40) was 63.3±6.25 years (95% CI: 61.3–65.3), with a mean antibody level of 2.17 IU/ml (95% CI: 1.47–2.81).

Conclusions: The ongoing occurrence of measles outbreaks, the presence of individuals with unknown vaccination and post-infection history, the low levels of protective post-vaccination antibodies among healthcare workers (34%; 45/133 in this study), along with the detection of protective antibody levels in all tested individuals with unknown history (100%; 40 participants), underscore the need for continued epidemiological monitoring. Timely vaccination and/or revaccination strategies are essential for maintaining population immunity.