The vast majority of COviD-19 candidate vaccines are designed to target the sars- Cov-2 spike (s) protein, but the precise vaccine-mediated immune correlates of protection remain to be determined. two recent reports from the Oxford COviD-19 vaccine team detail the immune outcomes observed in a phase I/II trial of their ChAdOx1 nCov-19 vaccine, in which volunteers received a single standard dose or various two- dose regimens.