Prevalence of Inadequate Immunity to Measles, Mumps, Rubella, and Varicella in MLB and NBA Athletes

BACKGROUND: Multiple outbreaks of vaccine-preventable viral diseases have occurred in professional sports in recent years. Currently, there is no established protocol for vaccination or immunity screening for professional athletes. HYPOTHESIS: There are significant differences in the prevalence of inadequate immunity dependent on age, sport, country of birth, and participation in collegiate sports. STUDY DESIGN: Cross-sectional cohort study. LEVEL OF EVIDENCE: Level 4. METHODS: A sample of Major League Baseball (MLB) and National Basketball Association (NBA) players were screened for serologic evidence of immunity to measles, mumps, rubella, and varicella prior to the 2015 and 2016 seasons. The results were designated as adequate (immune) or inadequate (equivocal or nonimmune) based on laboratory criteria. Comparison with an age-matched control group was performed using data from the National Health and Nutrition Examination Survey (NHANES). RESULTS: A total of 98 athletes (62 MLB, 36 NBA) were screened. The prevalence of inadequate immunity for any virus was 35.5% in MLB players and 33.3% in NBA players. There was a significantly greater risk of inadequate immunity to rubella (risk ratio, 6.38; P < 0.01) and varicella (risk ratio, 4.21; P < 0.01) in athletes compared with the age-matched NHANES population. Our analysis did not reveal differences in rates of immunity based on sport, country of birth (US born vs international), or participation in college athletics. There was a lower rate of inadequate immunity to varicella with increasing age (odds ratio, 0.72; P = 0.05). CONCLUSION: One-third of athletes studied had inadequate immunity to 1 of the 4 viruses tested. Younger players had a significantly greater risk of inadequate immunity to varicella. Birth outside the US and lack of participation in college athletics were not found to influence immunity rates. CLINICAL RELEVANCE: These results can inform the development of future screening programs to prevent outbreaks of viral infections in professional athletes.