MHRA said the mRNA-based shot that targets the Omicron BA.4 and BA.5 sub-variants as well as the original coronavirus strain was found to meet safety, quality and effectiveness standards.

The British authority had earlier approved the American/German partners’ bivalent vaccines targeting the omicron BA.1 sub-variant as well as a similar product made by US biotech Moderna.

EU healthcare regulator European Medicines Agency (EMEA) cleared the retooled Pfizer-BioNTech bivalent shot last month. The US Food and Drug Administration (FDA) and HealthCanada also have already given the nod.

"All approved Covid booster vaccines help to improve the protection obtained from earlier doses of the vaccine and help give longer-term protection against getting seriously ill from Covid-19," said the MHRA , which also signed off on the Novavax protein-based Covid shot as a booster for those who received mRNA shots as their primary series

Updated data from a Phase 2/3 clinical trial with Pfizer/BioNTech‘s omicron-adapted vaccine targeting BA.4/BA.5 released late last week are said to have shown substantially higher immune responses in trial participants compared with those who received the companies’ original Covid vaccines.

The vaccine makers said the results reinforce the previously reported early clinical data measured seven days after a booster dose of the bivalent vaccine, as well as the pre-clinical data. This suggeststhat a 30-µg booster dose of the adapted bivalent vaccine may induce a higher level of protection against the omicron BA.4 and BA.5 sublineages than the original vaccine, they said.

A small US study conducted in October by Columbia University and the University of Michigan in the US before the manufacturers’ detailed trial data was released appeared to show an insignificant difference between the original Pfizer/BioNTech vaccine and the bivalent booster three to five weeks after the last immunization.

At the time David Ho, the study’s senior author, suggested that the apparently lackluster results for bivalent boosters could be due to imprinting, which means that the immune system most strongly remembers the first version of a virus it encounters. After it mutates, the response to a vaccine, even one targeting newer strains, may still be tilted toward fighting the original pathogen.

Pfizer and BioNTech meanwhile have kicked off Phase1 trials of their combination vaccine candidate for influenza and Covid. This marries their quadrivalent modRNA-based influenza candidate the omicron-adapted Covid platform.

Author: Dede Williams, Freelance Journalist