Safety and immunogenicity of seven COVID-19 vaccines as a third dose (booster) following two doses of ChAdOx1 nCov-19 or BNT162b2 in the UK (COV-BOOST): a blinded, multicentre, randomised, controlled, phase 2 trial

All study vaccines boosted antibody and neutralising responses after ChAd/ChAd initial
course and all except one after BNT/BNT, with no safety concerns. Substantial differences
in humoral and cellular responses, and vaccine availability will influence policy
choices for booster vaccination.