A single-blind, randomised, phase II UK multi-centre study to determine reactogenicity and immunogenicity of booster vaccination against ancestral and novel variants of SARS-CoV-2 (COV-BOOST)

As of April 8th 2021 the MHRA in the UK has granted Regulation 174 approval for emergency use of 3 vaccines for protection against COVID-19 in the UK, including the mRNA vaccines BNT162b2 (Pfizer) the mRNA-1273 (Moderna) vaccine, and the chimpanzee adenovirus vector vaccine ChAdOx1-nCov19 (AstraZeneca/Oxford). So far over 30 million people in the UK have received at least one dose of either BNT162b2 or ChAdOx1-nCov19, with supplies of the mRNA-1273 expected imminently. Annual or seasonal booster vaccination for high risk groups is thought likely to be required, especially in light of the emergence of new variants of the SARS-CoV-2 virus. There is concern from studies in South Africa and elsewhere that existing vaccines may be less effective against these variant strains. It is currently unclear which booster vaccine schedule will provide the best safety profile and immune responses, according to which vaccine was originally given. The Joint Committee for Vaccination and Immunisation and UK Chief Medical Officers need timely information regarding the effects of different booster vaccinations on the safety profile and immunity to previous and new variants of SARS-CoV-2 in order to inform national policy for autumn and winter 2021. This study will determine the immune responses provided from different booster vaccinations given a minimum of 3 months from the 2nd dose of an initial course of AstraZeneca/Oxford or Pfizer vaccines.