Evaluation of RIT 4237 bovine rotavirus vaccine in newborn infants: correlation of vaccine efficacy to season of birth in relation to rotavirus epidemic period

A single oral dose of bovine rotavirus vaccine RIT 4237 or placebo was given to 2 groups of 5-day-old infants, born in October 1984 (n = 244) and June 1985 (n = 245), who remained in follow-up for 2.8 and 2.0 years, respectively. The vaccine had no effect on the total number of detectable episodes of rotavirus diarrhoea: there were 22 cases in the vaccinees and 24 in the placebo recipients in the October group and 18 and 16 respectively in the June group. However, vaccination decreased significantly the clinical severity of rotavirus diarrhoea, as assessed by a numerical score 0-20; this vaccine effect was much greater in the infants born in October. The mean severity scores for vaccine and placebo recipients were 4.55 and 10.75 respectively in the October group (p less than 0.0001, t-test) and 8.2 and 11.6 respectively in the June group (p = 0.010, t-test). Vaccine-induced clinical protection against rotavirus diarrhoea did not correlate well with serological response after vaccination, but showed good correlation to the presence of rotavirus antibodies before the rotavirus epidemic season. It is concluded that bovine rotavirus vaccine is more efficacious when given immediately before the rotavirus epidemic season: the vaccine effect may be amplified by exposure to wild rotaviruses during the season.