A Cochrane review [Abstract] 1 included one cluster-RCT (with 157 259 participants) and four RCTs of individuals (1 917 participants). The cluster-RCT from the former USSR showed that, compared with no vaccine, a live-attenuated vaccine (called STI) protected against clinical anthrax whether given by a needleless device (RR 0.16; 102 737 participants, 154 clusters) or the scarification method (RR 0.25; 104 496 participants, 151 clusters). Confidence intervals were statistically significant in unadjusted calculations, but when a small amount of association within clusters was assumed, the differences were not statistically significant.
The four RCTs (of individuals) of inactivated vaccines showed a dose response relationship for the anti-protective antigen IgG antibody titre. Intramuscular administration was associated with fewer injection site reactions than subcutaneous injection, and injection site reaction rates were lower when the dosage interval was longer.
Comment: The quality of evidence about the effectiveness of inactivated vaccines is indirect (evidence on immunologic response, but not on the prevention of clinical disease). However, RCT:s to assess the effectiveness of these vaccines in protecting against anthrax disease are unlikely to be feasible because the disease is uncommon. The quality of evidence about the effectiveness of live -attenuated vaccine is downgraded by study quality (inadequate cluster analysis).
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