Military personnel often receive several vaccinations as they prepare for service in an environment with many endemic diseases. People have expressed concerns that multiple vaccinations prior to and during Gulf War service may have caused adverse health effects.

Certain multiple vaccination regimens can lead to suboptimal antibody responses, but there is little evidence, largely because of a lack of active monitoring, of adverse clinical or laboratory consequences beyond the transient local and systemic effects seen frequently with any vaccination.

A group of 99 employees at Fort Detrick, Maryland, who received many vaccinations related to occupational requirements, were followed for up to 25 years to investigate the potential subclinical effects of intensive vaccination. The participants underwent physical examinations and laboratory testing in 1956, 1962, and 1971 (Peeler et al., 1958, 1965; White et al., 1974). No clinical sequelae attributable to intense long-term immunization could be identified in this cohort. None of the subjects suffered unexplained clinical symptoms requiring them to take sick leave that could be attributed to the vaccination program. There was some evidence of a chronic inflammatory response, as characterized by certain laboratory test abnormalities. However, these changes cannot necessarily be attributed to the vaccinations, because the workers studied were occupationally exposed to a number of virulent microbes. This series of longitudinal clinical studies had several shortcomings. However, the studies were valuable because careful monitoring did not disclose any evidence of serious unexplained illness in a cohort that received a series of intense vaccination protocols over many years.

Several studies of U.K. Gulf War veterans provide some limited evidence of an association between multiple vaccinations and long-term multisymptom outcomes, particularly for vaccinations given during deployment (Unwin et al., 1999; Hotopf et al., 2000). There are some limitations and confounding factors in these studies, and further research is needed.