A team studying the effects of third vaccines doses said the body's T cell immune response meant that protection from hospital admission and death seemed more likely.
The study also backs up the UK’s decision to offer Pfizer or Moderna as a third shot, with mRNA jabs leading to the most significant rise in immunity levels.
Listen to the Coronavirus podcast:
Professor Saul Faust, trial lead and director of the NIHR Clinical Research Facility at University Hospital Southampton NHS Foundation Trust, said the CovBoost study had shown that six different vaccines are safe and effective as booster doses for people who have already had two doses of AstraZeneca or Pfizer/BioNTech.
The six vaccines tested as a third dose were AstraZeneca, Pfizer/BioNTech, Moderna, Novavax, Janssen (made by Johnson and Johnson) and CureVac (which has ceased production).
“All of the vaccines in our study do show a statistically significant boost… RNA (Pfizer and Moderna) very high, but very effective boosts from Novavax, Janssen and AstraZeneca as well,” Prof Faust said.
He added that the vaccines worked well against existing variants, although Omicron was not tested in the study.
However, experts think that T cell immunity – which was studied alongside antibodies in the research – could also play a significant role in fending off the variant.
T cells play a key role and work alongside antibodies in the immune system to target viruses.
“Even though we don’t properly understand its relation to long-term immunity, the T cell data is showing us that it does seem to be broader against all the variant strains, which gives us hope that a variant strain of the virus might be able to be handled, certainly for hospitalisation and death if not prevention of infection, by the current vaccines,” Prof Faust said.
He said T cell response was not just focused on the spike protein but “are recognising a much broader range of antigens that might… be common to all of the variants.”
Asked specifically about Omicron, he said: “Our hope as scientists is that protection against hospitalisation and death will remain intact.”
Samples from the study have now been passed to the UK Health Security Agency (UKHSA) to look at how well the Omicron variant can be neutralised by vaccines.
Jonathan Ball, professor of molecular virology at the University of Nottingham, said of the new research: “This is a fantastic study and it’s great to finally see the data that was no doubt pivotal in deciding the UK’s vaccine booster approach.
“The data clearly shows that all boosters provided a lift to at least one aspect of your Covid immunity, and that side effects were, on the whole, mild.
“We still don’t know how this increase in immunity translates into protection, especially against serious disease, but I am still convinced that our vaccines will continue to provide the protection that we need.”
The new CovBoost trial, published in The Lancet, involved 2,878 people aged 30 or over receiving a booster 10 to 12 weeks after their initial two-dose vaccination.
Overall, there were 13 different groups testing the boosters or acting as controls, with controls given a meningitis vaccine.
Immunity was then assessed after 28 days, with experts saying that more data will be published in the future on the immunity results three months and one year after receiving boosters.
All seven vaccines posed no safety concerns, according to the study, with fatigue, headache and sore arm the most commonly reported issues.
Prof Faust said: “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.”