TY21A ORAL ATTENUATED SALMONELLA TYPHI VACCINE ADVERSE REACTION PROFILE IS SUPERIOR TO PARENTERAL KILL VACCINE -- INVESTIGATOR TELLS FDA ADVISORY CMTE
TY21A oral attenuated salmonella typhi vaccine has a superior adverse reaction profile to parenteral kill acetone vaccine, University of Maryland School of Medicine Center for Vaccine Development Director Myron Levine, MD, told FDA's Vaccines and Related Biological Products Advisory Cmte. at its May 29 meeting. Citing recent studies in Chile, as well as published studies over the last decade since the vaccine strain's development, Levine stated that TY21A "is not associated with adverse reactions -- - a very, very different situation from what one sees anywhere in the Third World where one gives parenteral kill vaccine." Levine presented the results of three TY21A studies in Chile to the cmte., after which the cmte. met in closed session to review the pending license application for the oral vaccine. The sponsor of the vaccine was not disclosed. The vaccine was developed by Swiss Serum and Vaccine Institute-Berne Research and Production Director Rene Germanier, MD. The field trials in Chile were supported by grants from the World Health Organization (WHO) and the Pan American Health Organization, and a research contract from the U.S. Army Medical Research and Development Command. Oral Vaccine Efficacy Rate Is Above 50%,Studies In Chile Demonstrate One study of TY21A in school children in Chile, Levine said, found "no difference in the incidence of adverse reactions such as vomitting, abdominal pain, headache, diarrhea and constipation . . .between vaccine and placebo." Levine added that other studies show "no significant adverse reactions" with TY21A vaccine. Commenting on the incidence of adverse reactions with parenteral kill typhoid vaccine, Levine said the vaccine "is not used in virtually any developing country as a public health tool in a routine manner because, although it is efficacious, it is highly reactogenic." Reporting on the first efficacy trial with the enteric-coated formulation of the TY21A vaccine, Levine explained that 90,000 of 130,000 school children in Northern Santiago, Chile, were randomized to receive either two doses of the vaccine, one dose of the vaccine and one dose placebo, or two doses placebo. The 33-month study, begun in May 1982, found that two doses of vaccine "diminished the attack rate of typhoid by 55%," while one dose "gave only 20% protection," and placebo treated children had a typhoid rate equivalent to that of children not given vaccine. In a second Chile trial, Levine said: "The success rate for three [entericcoated] doses given within a week was 56% vaccine efficacy and 51% if the enteric capsules were separated by the three doses. Gelatin bicarbonate formulation ranged in efficacy from 5 to 18% -- it virtually was not effective. The attack rate in the placebo group over these 18 months was 155 cases per 100,000, a high incidence rate." Asked by the cmte. if 50% efficacy was sufficient, Levine responded: "I strongly suspect that acetone kill vaccine in Chile would resemble the experience in Tonga" where the kill vaccine was 40% efficacious. "I think Chile is the most extreme test of a vaccine," Levine continued. Levine acknowledged that there is a "preliminary glimmer [which is] very bothersome because there's not an immune response to TY21A, and [it] remains to be seen the bearing this has in terms of either antigens that are being carried." That is "not to say they're not protected," he added, "it's just to say that we have not been able to so far measure an immune response."
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