Objective To determine the outcome of anthrax immunisation.

Methods Adverse reactions (occurrence, nature, severity and incapacity) and immune responses to a voluntary programme of anthrax immunisation at 0, 3, 6, and 24 weeks were monitored by questionnaire and voluntary blood sampling in 129 members, including 24 immunised 7 years previously (immunes), of a military field hospital alerted for possible deployment.

Results Follow-up was complete in 85%. Ninety-eight (76%) received the first anthrax immunisation. Uptake was greater (p=0.015) in immunes. Initial prevalence of adverse reaction was 63%. Subsequent uptake and adverse reaction dwindled significantly (p<0.001). Only 28 (22%) were immunised at 24 weeks. Proportions reporting adverse reactions following the initial immunisation were greater in immunes (p=0.046) and officers (p=0.02). There was no significant (p=0.36) correlation between uptake of immunisation and prevalence of adverse reaction. Antecedent adverse reaction did not reduce the proportion of participants accepting immunisation subsequently. The nature of adverse reactions (47% local, 24% systemic and 27% both ) and severity were the same throughout. Forty-five percent of adverse reactions caused incapacity. Seventy-four percent of these had pain in the injected arm (± systemic symptoms) which prevented lifting or driving for 48 hours in 63%. Immune responses were greater in immunes.

Conclusions It was concluded that anthrax immunisation results in a higher than expected prevalence of adverse reaction with initial incapacity of military significance affecting 18%. Greater immune responses may increase adverse reaction but this does not affect acceptance of anthrax immunisation. Poor completion rates necessitate development of a new anthrax immunisation strategy.