LONDON – COVID-19 vaccines made by Pfizer and Moderna that use mRNA technology produce the biggest boost in antibody levels when given 10-12 weeks after the second dose, a new British study has found.

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The “CoV-Boost” Study was cited by British officials when they announced that Pfizer and Moderna had been prioritized for use in the country’s booster campaign, but the data has only been made publicly available.

The study found that six of the seven boosters tested showed increased immunity after initial vaccination with Pfizer-BioEntech’s vaccine, while all seven showed increased immunity when given after two doses of AstraZeneca’s vaccine.

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“A third dose will be effective in many of the vaccines we have tested and in many different combinations,” Professor Saul Faust, an immunologist at the University of Southampton and the head of the trial, told reporters.

The study, published late Thursday, found that either a full dose of Pfizer or a half dose or a full dose of Moderna gave a strong boost to both antibody and T-cell levels, regardless of whether the person initially received Pfizer or AstraZeneca.

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“All four vaccination regimes widely deployed in the UK lead to essentially the same level of immunity and are likely to be equally effective,” said Professor Eleanor Riley, immunologist at the University of Edinburgh. He said the policy change in booster gaps was also backed by data.

“These data support the decision of the JCVI (Vaccine Committee) earlier this week to advance the booster dose to 3 months after the second vaccination.”

The study found that when AstraZeneca, Novavax, Johnson & Johnson and CureVac were given as boosters, they increased antibody levels to the initial vaccine, albeit to a small degree. However, while Valneva initially increased antibodies in people vaccinated with AstraZeneca, it did not promote Pfizer.

The COV-Boost study pre-dated the spread of the emerging Omicron variant of the concern, and Faust said he had shared samples with the UK Health Protection Agency to generate data on Omicron.

However, the study found that the booster shots also helped generate a broader T-cell response against beta and delta variants, which may play an important role in long-term protection.

A separate study by Imperial College London in How Early Exposure to SARS-CoV-2 Shapes Immune Responses, published late on Thursday, similarly found a good T-test for both alpha and delta after infection following vaccination. Cell response was found.

(Reporting by Alistair Smout; Editing by Bernadette Baum and Mark Heinrich)