Fig. 1: Study designs.

Study 1 was conducted in bovine RSV (bRSV)-seronegative (Ab−) colostrum-deprived calves. Study 2 was conducted in Ab− calves fed bRSV antibody-negative colostrum, and in bRSV-seropositive (Ab+) calves fed Ab-positive colostrum. Animals (n = 7 to 9/group) received 1 or 2 doses (1D or 2D, respectively) of either ChAd155-RSV vaccine or placebo (phosphate-buffered saline; controls). Corresponding vaccine and control groups followed the same treatment/challenge schedules after either a short (4 weeks) or a long (16 weeks) duration of immunity (short DOI or long DOI, respectively). Short or long DOI calves were recruited in two separate cohorts to arrange the challenge on the same calendar day.