COV-BOOST trial data show value of fourth dose

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 a 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."