ROTAVIRUS INFECTION IN INFANTS AS PROTECTION AGAINST SUBSEQUENT INFECTIONS

Background Rotavirus is the leading cause of severe diarrhea in infant s. To provide a base line for assessing the efficacy of rotavirus vacc ines, we evaluated the protection that is conferred by natural rotavir us infection. Methods We monitored 200 Mexican infants from birth to t wo years of age by weekly home visits and stool collections. A physici an assessed the severity of any episodes of diarrhea and collected add itional stool specimens for testing by enzyme immunoassay and typing o f strains. Serum collected during the first week of life and every fou r months thereafter was tested for antirotavirus IgA and IgG. Results A total of 316 rotavirus infections were detected on the basis of the fecal excretion of virus (56 percent) or a serologic response (77 perc ent), of which 52 percent were first and 48 percent repeated infection s. Children with one, two, or three previous infections had progressiv ely lower risks of both subsequent rotavirus infection (adjusted relat ive risk, 0.82, 0.40, and 0.34, respectively) and diarrhea (adjusted r elative risk, 0.23, 0.17, and 0.08) than children who had no previous infections. No child had moderate-to-severe diarrhea after two infecti ons, whether symptomatic or asymptomatic. Subsequent infections were s ignificantly less severe than first infections (P=0.024), and second i nfections were more likely to be caused by another G type (P=0.054). C onclusions In infants, natural rotavirus infection confers protection against subsequent infection. This protection increases with each new infection and reduces the severity of the diarrhea. (C) 1996, Massachu setts Medical Society.