Results of the COV-BOOST multicenter phase II trial show that the booster dose of six vaccines generated a strong immune response in persons who had completed their primary vaccination with either the Oxford-AstraZeneca vaccine or the Pfizer-BioNTech vaccine. The vaccines studied included Oxford-AstraZeneca, Pfizer-BioNTech, Novavax, Janssen, Moderna, Valneva and Curevac. The side effects with all vaccines were minor.

For the trial, 2878 participants were enrolled in the month of June; they had received two doses of either Pfizer or Oxford-AstraZeneca (first dose in December 2020, January 2021 or February, 2021). The study was conducted at 18 sites in the UK. “Participants had received their first doses of Oxford-AstraZeneca or the Pfizer-BioNTech vaccines in December 2020, or January, or February, and second doses at least 70 days (for Oxford–AstraZeneca) or 84 days (for Pfizer-BioNTech)” before study entry. Anti-spike protein IgG generated was evaluated at 28 days.

In persons who had taken the Oxford vaccine as their primary vaccination, the mean anti-spike protein antibody (IgG) after 28 days ranged from 1.8 times in the half Valneva group to 32.3 higher in the m1273 group. After two doses of the Pfizer-BioNTech vaccine, the booster dose increased the spike IgG (mean) from 1.3 times in the half Valneva group to 11.5 times in the m1273 group. “GMRs for wild-type cellular responses compared with controls ranged from 1.0 for half VLA to 4.7 for m1273 vaccine”. The response to booster doses were comparable between the participants aged 30–69 years and those aged 70 years and older. The most common reported side effects after booster dose were injection site pain, muscle soreness and fatigue.

This trial has demonstrated the effectiveness of all vaccines tested in boosting immunity following initial immunization with Oxford-Astra and Pfizer vaccines. All the booster vaccines studied were found to increase the immune response 28 days after initial vaccination with both Oxford-AstraZeneca vaccine doses. After the two Pfizer vaccine doses, all vaccines except Valneva boosted the immune response. All vaccines were found safe to be used.

Reference

1. Munro APS, et al. 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. The Lancet. December 02, 2021, DOI: https://doi.org/10.1016/S0140-6736(21)02717-3.