Anthrax is a bacterial infection that usually affects animals. Anthrax is not common in humans, but it can be acquired through breaks in the skin, from contaminated food, and through inhalation of bacteria. Human anthrax is often serious and can cause high rates of death. Various types of anthrax vaccines have been developed to protect those who may be exposed to the infection. The authors of this review wanted to evaluate the benefits and harms of vaccines for preventing anthrax. They identified four recent smaller randomized controlled trials of individuals and an older large cluster-randomized controlled trial with over 150,000 participants. The cluster trial provided limited evidence that a vaccine, based on a strain of live anthrax organisms incapable of causing disease, was effective in preventing cutaneous anthrax. More recent types of vaccines tested in the smaller trials, also based on inactivated components of the anthrax bacterium, appear to have few adverse events and to stimulate a good immune response. Several randomized controlled trials testing these newer vaccines are currently in progress. They will provide further information on the immunogenicity and safety of different vaccine regimens to be used for people at risk of anthrax exposure.
One cluster-RCT provides limited evidence that a live-attenuated vaccine is effective in preventing cutaneous anthrax. Vaccines based on anthrax antigens are immunogenic in most vaccinees with few adverse events or reactions. Ongoing randomized controlled trials are investigating the immunogenicity and safety of anthrax vaccines.
Anthrax is a bacterial zoonosis that occasionally causes human disease and is potentially fatal. Anthrax vaccines include a live-attenuated vaccine, an alum-precipitated cell-free filtrate vaccine, and a recombinant protein vaccine.
To evaluate the effectiveness, immunogenicity, and safety of vaccines for preventing anthrax.
We searched the following databases (November 2008): Cochrane Infectious Diseases Group Specialized Register; CENTRAL (The Cochrane Library 2008, Issue 4); MEDLINE; EMBASE; LILACS; and mRCT. We also searched reference lists.
We included randomized controlled trials (RCTs) of individuals and cluster-RCTs comparing anthrax vaccine with placebo, other (non-anthrax) vaccines, or no intervention; or comparing administration routes or treatment regimens of anthrax vaccine.
Two authors independently considered trial eligibility, assessed risk of bias, and extracted data. We presented cases of anthrax and seroconversion rates using risk ratios (RR) and 95% confidence intervals (CI). We summarized immunoglobulin G (IgG) concentrations using geometric means. We carried out a sensitivity analysis to investigate the effect of clustering on the results from one cluster-RCT. No meta-analysis was undertaken.
One cluster-RCT (with 157,259 participants) and four RCTs of individuals (1917 participants) met the inclusion criteria. 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 (anthrax vaccine absorbed and recombinant protective antigen) 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.