Varicella susceptibility and vaccine use among young adults enlisting in the United States Navy

Primary varicella infection, or chicken pox, is a threat to all young adults who join the United States (U.S.) military if they fail to develop immunity prior to enlistment. Historically, outbreaks of chicken pox have caused marked morbidity and impaired military readiness. In December 1996, the U.S. Navy began performing serologic testing for varicella among all new recruits, and vaccinating those found to be seronegative. We evaluated results of the screening program in its first 4 years, and used multivariable logistic regression modeling to describe factors associated with varicella susceptibility. Cases of chicken pox were tracked among all military services before and after program implementation. More than 190,000 young adults enlisted in the U.S. Navy between 1997 and 2000. Recruits originated from all 50 states and several foreign countries; 84% were male, and their average age was 19 years. Seven percent were found to be susceptible (sero-negative) to varicelia. In multivariable modeling, race/ethnicity was associated with susceptibility, but age, gender, and home state were not. The overall incidence of chicken pox in the Navy was reduced by more than 80% after initiation of the screening-vaccination program. A successful varicella screening-vaccination program has been implemented in the U.S. Navy. Results of serologic screening undertaken on this large number of young adults may be useful in tracking the changing epidemiology of varicella in the general population in the post-vaccine era.