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Many decades into the vaccine era, we still are being surprised by new patterns in old childhood diseases. Two studies address these changing patterns.
In one study, researchers examined the largest U.S. mumps outbreak in 2 decades, which erupted in eight midwestern states in 2006. Almost 7000 people were affected, with estimated incidence in 18- to 24-year-olds that was higher than in all other age groups combined. Most of those in that age group had acquired the disease on college campuses, and most had received two childhood doses of mumps vaccine. To explain secondary vaccine failure on this large a scale, the researchers hypothesized a combination of waning vaccine immunity, lack of natural boosting by circulating wild virus, and sudden introduction of disease, possibly from a simultaneous large outbreak in the U.K.
In another study, researchers addressed the continued occurrence of varicella cases despite widespread vaccination. Researchers examined postvaccination antibody in 148 healthy children: Only 76% seroconverted after a single dose of vaccine, a rate of primary vaccine failure significantly higher than that in many previous reports in which a different antibody assay was used. These data, from the laboratory in which much of the original vaccine work had been performed, support the booster-dose varicella vaccine recently recommended by the Advisory Committee on Immunization Practices.
Dayan GH et al. Recent resurgence of mumps in the United States. N Engl J Med 2008 Apr 10; 358:1580.
Michalik DE et al. Primary vaccine failure after 1 dose of varicella vaccine in healthy children. J Infect Dis 2008 Apr 1; 197:944.
Comment
Despite effective and widely implemented vaccines, childhood diseases still circulate and raise new questions, as patterns of herd immunity and background circulating disease evolve. While researchers monitor national patterns, practitioners should remember to keep all the vaccine-preventable diseases on their diagnostic radar.