Rotavirus Infection in Brazil: Epidemiology, Immunity, and Potential Vaccination.
Worldwide, it is estimated that rotaviruses cause more than 125 million diarrheal episodes and nearly 1 million deaths per year among infants and young children. In Brazil, these agents have been associated with 13%-40% of cases of acute diarrhea affecting pediatric in-patients and outpatients. Longitudinal community-based studies involving children followed from birth to the age of three years, yielded an average of 0.3 rotavirus-related episodes of diarrhea per child per year. While seasonality of rotavirus infections is not evident in the more northern tropical areas, a peak incidence during the driest months (May to September) has been noted in Brazil's central and southern states. All four epidemiologically important rotavirus serotypes have been identified in Brazil, with Gl and G2 accounting for about two-thirds of typed strains. The recent characterization of G- and P- genotypes has demonstrated that predominant strains are essentially the same as those most commonly identified worldwide: taken together, P[S]G1 and P[4]G2 rotaviruses account for over 50% of genotyped strains. In addition, the occurrence of unusual types, such as P[8]G5, and mixed infections, have been reported in about 10% and 20% of diarrheal cases, respectively. Outbreaks of rotavirus diarrhea have been reported in both urban and remote communities, G2 type being reported to cause severe gastroenteritis among adults and children. Among Indian populations the clinical attack rate has approached 90%. Rotavirus group C has been associated with outbreaks of diarrhea in day-care centers, yielding clinical attack rates of nearly 50%. Seroprevalence studies in several regions in Brazil indicate that at least 70% of children aged 4-5 years have antibodies to rotavirus. It has also been demonstrated in longitudinal studies that heterotypic immune response in a primary infection may be an intrinsic property of the rotavirus strain. A tetravalent rhesus-human reassortant rotavirus vaccine (4 x 10,000 pfu/dose) has been evaluated in northern Brazil with the following main results: a) the vaccine was safe with only low-grade fever on days 3-5 in 2%-3% of vaccinees after the first dose; b) an IgA antibody response occurred in 58% of vaccinees and 33% of placebo recipients; and c) the overall vaccine efficacy was 35% (p = 0.03) against any rotavirus diarrhea for the 2-year study period, but reached 57% (p = 0.008) during the first year of follow-up. In view of findings indicating strain diversity throughout Brazil, a country-wild surveillance system is urgently needed to monitor circulating rotavirus strains.