V12* England Safety and Immunogenicity of the ChAdOx1 nCoV-19 COVID-19 Vaccine Against SARS-CoV-2

Phase 1/2, single-blind, randomized controlled trial in five trial sites in the UK of a chimpanzee adenovirus-vectored vaccine (ChAdOx1 nCoV-19) expressing the SARS-CoV-2 spike protein compared with a meningococcal conjugate vaccine (Men ACWY) as control. 

Healthy adults aged 18–55 years with no history of laboratory confirmed SARS-CoV-2 infection or of COVID-19-like symptoms were randomly assigned (1:1) to receive ChAdOx1 nCoV-19 at a dose of 5 × 1010 viral particles or Men ACWY as a single intramuscular injection. 

Between April 23 and May 21, 2020, 1077 participants were enrolled and assigned to receive either ChAdOx1 nCoV-19 (n=543) or Men ACWY (n=534), ten of whom were enrolled in the non-randomized ChAdOx1 nCoV-19 prime-boost group.

Neutralizing antibody responses against SARS-CoV-2 were detected in 32 (91%) of 35 participants after a single dose when measured in MNA80 and in 35 (100%) participants when measured in PRNT50. 

After a booster dose, all participants had neutralizing activity (nine of nine in MNA80 at day 42 and ten of ten in Marburg VN on day 56). 

ChAdOx1 nCoV-19 showed an acceptable safety profile, and homologous boosting increased antibody responses.

Many phase 3 studies fail because of incorrect identification of the dose that best balances safety and efficacy.7 The dosing regimen for this mRNA vaccine is still under study. The 250-μg dose did not appear to be associated with markedly higher antibody titers than the 100-μg dose, but it was associated with a higher proportion of severe systemic adverse events.