Young healthcare personnel (HCP) were found to be less likely to have detectable measles antibodies due to either declining vaccination rates or significant waning of vaccine-induced immunity below the threshold of clinical protection, according to the results of a study recently published in Clinical Infectious Diseases.

Although measles was essentially eliminated in the United States 20 years ago, a resurgence in the number of cases has prompted a nationwide intensification of measles-specific prevention measures. From 2001 to 2014, 78 measles cases were reported in US healthcare facilities, including 29 HCP, 19 of whom had presumptive evidence of immunity as determined by criteria established by the Centers for Disease Control and Prevention (CDC). Presumptive evidence of immunity based on CDC criteria is either 2 doses of the measles, mumps, and rubella (MMR) vaccine for HCP born in 1957 or later OR 2 positive measles immunoglobulin G (IgG) antibody test results. According to the CDC, only 10 states have enacted laws requiring HCP to demonstrate immunity to MMR. Although large seroprevalence studies conducted on US HCP in the 1990s showed that approximately 6.5% of HCP lacked measurable measles antibodies, similar assessments for US HCP born after 1985 who would have received 2 MMR doses in childhood are lacking. Therefore, at Memorial Sloan Kettering Cancer Center (MSKCC) in New York City, a team of researchers determined the age-specific seroprevalence of measles antibody in a large cohort of newly employed HCP.

Over a 10-year period, 12,349 HCP began working at MSKCC and were included in this analysis. Proof of immunity for measles at the time of hire is required for all healthcare workers in the state of New York, and presumptive evidence of immunity is based on the CDC criteria. At MSKCC, all new hires undergo serologic assessment regardless of documentation or history of adequate vaccination. History of clinical measles is not considered proof of immunity, and HCP who lack immunization records or have negative titers must be vaccinated before their start date. All included individuals were tested for measles antibody (IgG) during their pre-employment clearance.

Results suggest that a wider adoption of requirements to increase MMR vaccination rates may be necessary for healthcare workers. In total, 78% of included individuals were aged between 20 and 39 years. The overall seroprevalence for measles was 85.7%. A statistically significant difference in serologic evidence of immunity across all age groups was documented. A 90% seropositivity for the measles antibody was identified for the 231 newly hired HCP who were older than 60 years. Seropositivity rates decreases as age decreased: 90.7% for 50 to 59 years, 89.6% for 40 to 49 years, 86.5% for 30 to 39 years, and 83.2% for 20 to 29 years. HCP aged 20 to 29 years had significantly higher odds of negative measles immunity when compared with their colleagues aged 30 to 39 years (odds ratio [OR]=1.29; P <.001); the same was observed when HCP aged 30 to 39 years were compared with those who were aged 40 to 49 years (OR=1.35; P =.002). No significant difference was observed in the odds of negative immunity when comparing HCP aged 40 to 49 years with those aged 50 to 59 years (P =.419).

Overall, the study authors conclude that, “While the clinical implications of waning antibodies in young HCP are not completely understood, our study results offer important considerations for prevention and management of measles exposure in HCP. This is especially relevant as policies and practices related to occupational exposures are revisited with the unprecedented worldwide resurgence of measles.”

Lower Rate of Seropositivity to Measles Among Younger Clinicians

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