Measles, Mumps Immunity Declining in Military Recruits

Measles and mumps immunity levels among US Air Force recruits don't seem high enough to prevent disease outbreak.

Measles and mumps immunity levels among US Air Force recruits don’t seem high enough to prevent disease outbreak.

Across 35,502 recruits entering basic training at Joint Base San Antonio-Lackland in Texas between April 2013 and April 2014, researchers found seroprevalence rates for measles, mumps, and rubella (MMR) antibodies were 81.6%, 80.3%, and 82.1%, respectively.

Each of these rates falls below herd immunity thresholds, which may not bode well for similar populations, the investigators noted.

College students, for instance, sleep and live close to each other just like recruits, and this type of environment increases the odds of disease transmission.

“If individuals entering the workforce and college across the nation have the same rates as the recruits, outbreaks of vaccine-preventable disease can be anticipated to continue,” said lead study author Air Force Lt. Col. Paul E. Lewis, III, MD, MPH, in a press release.

The MMR seroprevalence rates seen in this study were also lower than those reported in 2 previous papers.

The researchers pointed to a 1999 to 2004 National Health and Nutrition Examination Survey, which found that MMR seropositivity rates were 96%, 90%, and 89%, respectively, among the 1977 to 1986 birth cohort. They also cited a study that examined recruits between 2000 and 2004 and found that seroprevalence rates were 86.1%, 91.6%, and 94.8%, respectively.

Recruits aged 20 to 29 years were less likely to be seropositive for measles than their younger comrades aged 17 to 19 years. The results were the opposite for mumps and rubella, however, as older recruits aged 30 to 35 years had higher seropositivity than those aged 17 to 19 years.

MMR seropositivity was 4% to 6% higher among women, which the authors partially attributed to rubella vaccinations being especially encouraged for new mothers. Another factor could be increased immune response in women following flu vaccinations.

Nevertheless, both genders and almost all age groups had MMR seroprevalence rates below the thresholds to maintain herd immunity. Only those aged 30 to 35 years had mumps and rubella seroprevalence rates that achieved these thresholds, though no age group met the 85% threshold for measles.

When seroprevalence levels fail to meet these thresholds, disease outbreaks may ensue, the authors noted.

They suggested that poor vaccination uptake prior to entering the military may partially explain why rates were below herd immunity thresholds.

The Department of Defense’s current policy is to assume that an individual has mumps immunity if his or her measles and rubella antibody titers are positive. However, the researchers warned that the mumps vaccine may be less effective than the measles and rubella vaccines, and its efficacy can wane faster than the measles or rubella vaccines.

Thus, they encouraged the Department of Defense to use antibody titers for MMR and vaccinate recruits who show susceptibility to any 1 of the viruses.

Measles cases across the nation have seen an uptick since the virus was declared eliminated in 2000. Mumps cases have also increased—especially on college campuses.

While measles tend to stem from unvaccinated individuals, mumps often occur in those who were previously vaccinated but have weakened immunity.

The study was published in The American Journal of Preventive Medicine.