Typhoid vaccines: outlook for the future.

A new oral typhoid vaccine is undergoing trials among children in Egypt and Chile. Unlike the common injectable killed typhoid vaccine, which causes fever, pain and swelling at the injection site, this live oral vaccine has no side effects. It was developed from a new strain of typhoid, the Ty21a bacillus. The Chilean trials will attempt to determine the efficacy of Ty21a given in enteric coated capsules, to evaluate the efficacy of fewer doses, and to assess the efficacy of this vaccine in an area where typhoid is particularly widespread and lethal. 150,000 school children in Santiago, Chile will follow 5 protocols: 1) 3 doses within 1 week; 2) 3 doses with NaHC03 (sodium bicarbonate, an antacid) within 1 week, both in gelatin capsules; 3) 3 doses as in group 1, separated by 3 weeks; 4) 3 doses as in group 2, separated by 3 weeks; 5) placebo. Each dose contains 1-3 thousand million live, freeze-dried bacteria. Trials in Egypt where children took antacid before each of 3 doses of reconstituted vaccine showed 96% vaccine efficacy after 3 years of surveillance.