A new trial has tested seven different vaccines as the booster for people who received either two doses of the Pfizer-BioNTech or the Oxford-AstraZeneca vaccine. The data shows that all boosters were well tolerated, and all but one produced a strong immune response.
The results of the phase 2 trial are reported in The Lancet. Seven booster vaccines and one control were administered to the 2,878 participants in the UK, with the third doses given 10-12 weeks after the initial two-dose courses of the approved vaccine.
The data shows the immune response after 28 days – the effect of boosters on longer-term immunity is currently unknown. But, data collected after three months will be published in the new year.
The side effects are primarily muscle soreness, pain at the injection site, and fatigue, similar to those of the two-dose COVID-19 vaccines and other types of vaccinations. People over the age of 70 appeared to experience fewer side effects compared to the younger cohort.
"The side effect data show all seven vaccines are safe to use as 3rd doses, with acceptable levels of inflammatory side effects like injection site pain, muscle soreness, fatigue. Whilst all boosted spike protein immunogenicity after two doses of AstraZeneca, only AstraZeneca, Pfizer-BioNTech, Moderna, Novavax, Janssen and Curevac did so after two doses of Pfizer-BioNTech," Professor Saul Faust, trial lead and Director of the NIHR Clinical Research Facility, University Hospital Southampton NHS Foundation Trust, said in a statement.
"It's really encouraging that a wide range of vaccines, using different technologies, show benefits as a third dose to either AstraZeneca or Pfizer-BioNTech. That gives confidence and flexibility in developing booster programmes here in the UK and globally, with other factors like supply chain and logistics also in play."
The study has limitations due to the pandemic timelines. The boosters were given much earlier than current policy states, something being addressed in a trial amendment. The participants were also older than the general population (all were over 30) and were mostly white. Further work will be necessary.