Administering a fourth dose of an mRNA COVID-19 vaccine provides a stronger level of protection than a third dose, particularly in the over-70s, according to the latest readout from the UK COV-BOOST trial.
The trial showed that a second booster with the mRNA shots developed by Moderna and Pfizer/BioNTech given around seven months after the first booster is safe, and generates strong antibody and T-cell responses.
Experts say however it is likely that the protection is likely to wane quickly, as seen in other studies of the vaccines, and with levels of COVID-19 in decline among the population of many countries including the UK the need for a further booster round in the autumn remains uncertain.
The UK rolled out fourth doses to over-75s and other vulnerable people last month, but there’s no decision yet on whether the programme may be offered more broadly.
Israel and Germany meanwhile are among a group of other countries that have opted for broad rollout of another booster to all adults, but the European Commission said last month there is not yet enough evidence to warrant widespread use.
A green light for second boosters could be pivotal if Pfizer/BioNTech and Moderna are to meet their expectations for sales of the two mRNA-based shots in 2022.
The latest COV-BOOST findings are published in the Lancet Infectious Diseases journal, and according to the authors are the first data from a randomised trial of a second booster of Pfizer/BioNTech’s Comirnaty and Moderna’s SpikeVax vaccines.
The authors said “peak responses after the fourth dose were similar to, and possibly better than, peak responses after the third dose.”
They went on: “Our results for immunogenicity are also consistent with the little observational evidence on vaccine effectiveness available from Israel, which indicates increased protection against symptomatic infection and severe illness from a fourth-dose booster.”
The majority of people in the UK received their third vaccine last winter, in response to the rapid emergence of the Omicron variant of SARS-CoV-2.
Health secretary Sajid Javid said the study provides “further evidence underlining the importance of people coming forward for their booster as soon as they are eligible.”
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