Merck & Co Inc's investigational pentavalent rotavirus vaccine, Rotateq, demonstrated 100 per cent efficacy against severe rotavirus gastroenteritis and 74 per cent efficacy against rotavirus gastroenteritis of any severity in healthy infants in a dose-ranging study. The study results were presented at the annual meeting of the European Society for Pediatric Infectious Diseases (ESPID).

"The levels of protection demonstrated in this dose-ranging study with this investigational vaccine are encouraging," said Timo Vesikari, professor of virology, University of Tampere Medical School and lead investigator in the study. "Merck is currently conducting phase III clinical trials using this vaccine, including a study that has enrolled more than 65,000 infants, which will provide additional safety and efficacy data for evaluation."

Rotateq is an investigational oral pentavalent vaccine containing five human serotypes - G1, G2, G3, G4 and P1. The five serotypes account for at least 75 percent of rotavirus strains worldwide, although the prevalence of each serotype varies from one geographic area to another.

The single-center (multiple sub-sites), randomized, double-blind, placebo-controlled study evaluated 1,946 healthy infants who were randomly assigned to one of six groups: high-dose pentavalent, middle-dose pentavalent, low-dose pentavalent, quadrivalent or monovalent vaccine and placebo. The vaccines were administered in the study as a three-dose regimen given at one- to two- month intervals with the first dose given at age two months to eight months.

Among the five groups that received vaccine, protection against all rotavirus gastroenteritis, regardless of severity, during the first rotavirus season following vaccination ranged from 43 per cent - 74 per cent. The lowest level of protection was seen in the monovalent group while the highest level was shown in the middle-dose pentavalent group.

The number of cases of rotavirus gastroenteritis that developed across the six groups, including placebo, ranged from eight to 33. The lowest number of cases was seen in the quadrivalent group and the highest number was seen in the placebo group.

Among the five groups that received vaccine, protection against severe rotavirus gastroenteritis during the first rotavirus season following vaccination ranged from 88 per cent - 100 per cent. The lowest level of protection was seen in the monovalent group while the middle, low and high-dose pentavalent groups all demonstrated 100 per cent protection.

The number of cases of severe rotavirus gastroenteritis that developed across the six groups, including placebo, ranged from zero to eight. The middle, low and high-dose pentavalent and quadrivalent groups had zero cases of severe rotavirus gastroenteritis while the monovalent and placebo groups had one and eight respectively.

Children were evaluated for safety with regard to all adverse events for 42 days after each dose, with specific attention to fever, vomiting and diarrhea during the week after each dose. The incidence of adverse events, including fever, vomiting and diarrhea, seen in the study were not significantly different between the vaccine candidate and placebo groups. For evaluation of efficacy, parents of the infants in the trial were contacted every two weeks during the rotavirus season after vaccination and asked about episodes of gastroenteritis. Intussusception was not a clinical endpoint for this dose-ranging study.