Researchers from the Naval Health Research Center (NHRC) discussed ongoing surveillance for the adenovirus, a contagious pathogen that causes respiratory illness, among U.S. military recruits during basic training at the Military Health System Research Symposium (MHRSRS), Aug. 27.

In the mid-1990s, the adenovirus vaccine was discontinued at military recruit training commands throughout the Department of Defense (DoD), resulting in frequent respiratory illness outbreaks. The adenovirus was the most prevalent and widely spread virus in military training environments, infecting up to 80 percent of recruits and resulting in lost training time and increased medical care.

In 2011, the adenovirus vaccine was reinstated for military recruits after NHRC and the Walter Reed Army Institute of Research conducted a clinical trial that demonstrated its safety and efficacy. According to researchers with NHRC's operational infectious diseases team, after the live, oral vaccine for adenovirus types 4 and 7 was resumed, rates of adenovirus among recruits declined dramatically - cases went from 250 each week to two, on average. To date, other adenovirus serotypes - 3, 14, and 21 - that had previously caused illness in recruits have not re-emerged.

Because there was such a dramatic drop in adenovirus-related cases, NHRC researchers wanted to determine if the vaccine provided protection against these other adenovirus serotypes that have not re-emerged after vaccination reinstatement. Because the other serotypes were not detected by routine surveillance, they hypothesized the vaccine would provide similar coverage and induce immunity against the other non-vaccine serotypes.

To test their hypothesis, researchers obtained 100 paired blood serum samples-samples obtained from recruits before and after they received the adenovirus vaccine-to test for changes in the level of antibodies found in the blood produced by the immune system to fight infection after vaccination. Using cell culture based serological microneutralization assays, researchers quantifiably measured antibody endpoint titers, a measure of the amount of antibodies in the blood stream that is believed to be correlative with the body's immune response.

Findings revealed that titers in the recruits' blood before they were vaccinated were low against four of the five adenovirus types - 4, 7, 14, and 21. The titers from the second sample, which were taken at least four weeks after the recruits were vaccinated, showed increased protection against the vaccine types 4 and 7, but not against the other three non-vaccine serotypes tested. Even though the vaccine protected against types 4 and 7, there was little evidence that it provided protection against the other adenovirus serotypes.

Vaccination has dramatically decreased adenovirus-related illness and febrile respiratory rates in recruit population, resulting in less disruption and setbacks to training, reducing both the cost of health care and recruit training to the DoD. To understand why the other serotypes have not emerged among recruits after vaccination resumption and ensure recruits continue to be protected against outbreaks of this illness, researchers say further studies are needed.

As the DoD's premier deployment health research center, NHRC's cutting-edge research and development is used to optimize the operational health and readiness of the nation's Armed Forces. In proximity to more than 95,000 active-duty service members, world-class universities, and industry partners, NHRC sets the standard in joint ventures, innovation, and translational research.

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