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Updated:18/05/2022 18:40h
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Although all of them effectively prevent severe disease from VOCs, the research, published in the journal PLOS Medicine, suggests that people who receive a viral vector vaccine are more vulnerable to infection by the new variants.
As of March 2022, Covid-19 had caused more than 450 million confirmed infections and six million recorded deaths. The first approved vaccines in the US and Europe that protect against severe infection are those from Pfizer-BioNTech and Moderna, that deliver the genetic code, known as mRNA, to the cells of the bodywhile those from Oxford/AstraZeneca and J&J/Janssen are viral vector vaccines that use a modified version of a different virus – a vector – to deliver instructions to our cells.
The three vaccines are given as two separate injections a few weeks apart, and the J&J/Janssen vaccine is given as a single dose.
Marit J. Van Gils of the University of Amsterdam, the Netherlands, took blood samples from 165 health workers, three and four weeks after the first and second vaccination, respectively, and from J&J/Janssen at four, five and eight weeks after vaccination. Samples were collected before and four weeks after a Pfizer-BioNTech booster.
Four weeks after the initial two doses, antibody responses to the original viral strain of SARS-CoV-2 were highest in Moderna recipients, closely followed by Pfizer-BioNTech, and substantially lower in those who received vaccines of viral vectors.
In tests conducted against VOCs – Alpha, Beta, Gamma, Delta and Omicron – neutralizing antibodies were higher in recipients of the mRNA vaccine compared to those who received the viral vector vaccines. The ability to neutralize VOCs was reduced in all vaccine groups, with the greatest reduction against Omicron. The Pfizer-BioNTech boost increased antibody responses in all groups with substantial improvement against VOCs, including Omicron.
The researchers caution that their AstraZeneca group was significantly older, due to concerns about the safety of the vaccine in younger age groups. As immune responses tend to weaken with age, this could affect results. This group was also smaller because the Dutch government suspended its use for a time.
Van Gils concludes: “The four Covid-19 vaccines induce substantially different antibody responses.”
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