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expert reaction to COV-BOOST study investigating safety and immunogenicity of seven COVID-19 vaccines as a third dose following two doses of either Oxford-AstraZeneca or Pfizer

A study published in the Lancet looks at the safety and immunogenicity of seven COVID-19 vaccines as a third (booster) dose following two doses of Oxford-AstraZeneca or Pfizer-BioNTech vaccine in the UK.

This Roundup accompanied an SMC Briefing.


Prof Eleanor Riley, Professor of Immunology and Infectious Disease, The University of Edinburgh, said:

“The CovBoost study compared a number of different vaccines given as a booster approximately 3 months after the second of two doses of either the AZ or Pfizer vaccines.  Of particular relevance to the UK population are the results for boosting with either the Pfizer or Moderna vaccines.  No safety concerns were identified for any of the combinations studied.

“The good news is that whether you had AZ or Pfizer as your first two doses and whether you have Pfizer or Moderna as your booster, there is a marked increase in both your neutralising antibody concentration (on average a more than 20-fold increase) and your T cell response (on average an approximately 3 fold boost) against both the original Wuhan virus and against the Delta variant.

“After two primary doses and a booster, there is no meaningful difference in either neutralising antibody titres or T cell numbers between people who had either AZ or Pfizer as their first doses or Pfizer or Moderna as their boosters.  In other words, all four of the vaccination regimes most widely deployed in the UK lead to essentially the same levels of immunity and are likely to be equally effective.

“These data support the JCVI decision earlier this week to bring forward booster doses to 3 months after the second vaccination.  Immunogenicity data for boosters given 5 or 6 months after initial vaccination will emerge in the next few weeks but are likely to be broadly similar.

“The big unknown of course is how well these antibodies and T cells will cope with the omicron variant, but we should have data on that in the next week or so.”


Prof Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:

“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.

“The data also shows that an mRNA booster – such as Moderna or Pfizer – provided the best overall boost, irrespective of whether your first doses were mRNA or the AZ chimpanzee adenovirus vaccines.

“The use of inactivated virus or recombinant spike protein provided a boost for your antibody responses, but had less of an impact on your T-cells.

“Whilst variants, such as the delta variant, reduced the overall virus killing effect of antibodies, the T cell responses were pretty much unaffected.

“The fact that the mRNA vaccine boosts gave a marked increase in both antibodies and T cells is great news, especially now, when our attention has been grabbed by the emergence of the omicron variant.  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.”



‘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’ by Alasdair P S Munro et al. was published in the Lancet at 23:30 UK time on Thursday 2 December 2021.

DOI: 10.1016/S0140-6736(21)02717-3



All our previous output on this subject can be seen at this weblink:



Declared interests

Prof Eleanor Riley: “No COIs to declare.”

Prof Jonathan Ball: “Receipt of funding to develop next generation vaccines.”

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