Evaluation of the M37 human rotavirus vaccine in 2- to 6-month-old infants.

Human rotavirus strain M37, isolated from an asymptomatic neonate, was evaluated as a live oral vaccine in a double-blinded, placebo-controlled trial involving 282 infants ages 2 to 6 months. Either 10(4) or 10(5) plaque-forming units (PFU) of the M37 vaccine were tested in 102 and 39 infants, respectively. The vaccine was well-tolerated; fever on Days 1 to 7 after vaccination was recorded in 12 and 18% of infants receiving 10(4) and 10(5) PFU of the M37 vaccine, respectively, compared with 6% of those receiving placebo; none of the vaccinees developed diarrhea. A rotavirus IgA enzyme-linked immunosorbent assay serum antibody response was detected in 47 and 76% of the infants receiving the 10(4) and 10(5) PFU vaccines, respectively. No clinical protection against rotavirus diarrhea was observed in the group vaccinated with the 10(4) PFU dose; the number of infants vaccinated with 10(5) PFU was too small for evaluation of vaccine efficacy. The M37 vaccine in a titer of 10(4) PFU was found to be inadequate; the 10(5) PFU dose was more immunogenic than the lower dose and warrants further study for clinical efficacy.