Multiple vaccinations, health, and recall bias within UK armed forces deployed to Iraq: cohort study.

OBJECTIVE To assess the relation between self reported number of vaccinations received and health, and between numbers of vaccinations recorded from individuals' medical records and health. DESIGN First phase of a cohort study. SETTING UK armed forces personnel. PARTICIPANTS 4882 randomly selected military personnel deployed to Iraq since 2003 and a subset of 378 whose vaccination records were accessed. MAIN OUTCOME MEASURES Psychological distress, fatigue, symptoms of post-traumatic stress disorder, health perception, and multiple physical symptoms. RESULTS Personnel who reported receiving two or more vaccinations on a single day were more likely to report symptoms of fatigue (adjusted risk ratio 1.17, 95% confidence interval 1.05 to 1.30), show caseness according to the general health questionnaire (1.31, 1.13 to 1.53), and have multiple physical symptoms (1.32, 1.08 to 1.60). These associations were no longer significant when number of vaccinations recorded in individuals' medical records was used as the independent variable. CONCLUSIONS Multiple vaccinations given to personnel in the UK armed forces in preparation for deployment to Iraq are not associated with adverse health consequences when vaccinations are recorded objectively from medical records. Adverse health consequences associated with self reported multiple vaccinations could be explained by recall bias.