Rotavirus vaccines and vaccination in Latin America

Worldwide, rotaviruses account for more than 125 million cases of infantile gastroenteritis and nearly 1 million deaths per year, mainly in developing countries. Rather than other control measures, vaccination is most likely to have a major impact on rotavirus disease incidence. The peak incidence of rotavirus diarrhea occurs between 6 and 24 months of age. In developing countries, however, cases are not uncommon among children younger than 6 months. G serotypes 1 to 4 are responsible for most disease, but there are indications that in Brazil that G type 5 is of emerging epidemiological importance. Both homotypic and heterotypic responses are elicited during natural rotavirus infection, and the immunological response at the intestinal mucosal surface is probably the more consistent predictor of clinical immunity. With the primary objective of protecting children against life-threatening dehydrating diarrhea, many approaches to rotavirus vaccine development have been attempted. One vaccine, the tetravalent rhesus-human reassortant rotavirus vaccine (RRV-TV), was given licensing approval in the United States of America, introduced to the market, and later withdrawn. A number of studies have found better efficacy of RRV-TV in developed countries than in developing ones. Field trials with a 4 x 10(4) plaque-forming units (PFU) preparation of RRV-TV have been carried out in two countries in Latin America, Brazil and Peru. Those trials yielded protective efficacy rates against all rotavirus diarrhea ranging from 18% to 35%. Data from a large catchment trial in Venezuela with a higher RRV-TV dose, of 4 x 10(5) PFU/dose, indicated an efficacy rate of 48% against all rotavirus diarrhea and 88% against severe rotavirus diarrhea. It appears that breast-feeding does not compromise the efficacy of RRV-TV if three doses of the vaccine are administered. Similarly, possible interference of oral poliovirus vaccine with the "take" of the rotavirus vaccine can be overcome by giving three doses of the rotavirus vaccine or by using a higher-titer formulation of it. Wild enteroviruses, however, may cause primary rotavirus vaccine failure in developing countries. Studies in Peru with RRV-TV have shown a trend towards higher vaccine efficacy rates against "pure" (rotavirus-only) diarrheal episodes. Economic analyses made in the United States indicate that a vaccine that costs less than US$ 9 per dose would lead to a net savings in medical costs. To date, however, cost-benefit studies have not been done in developing countries. In the future, it is possible that some Latin American countries might adapt their polio production facilities to the preparation of rotavirus vaccines for human use. A year after RRV-TV was licensed for vaccination of infants in the United States, the occurrence of intussusception as an adverse event led to the vaccine's withdrawal from the market. The implications of that action, particularly for Latin America, will be addressed in this article, including the need to explore alternative rotavirus candidate vaccines, particularly through the conduct of parallel clinical trials in both developed and developing countries.