Britain, the first country to approve a coronavirus vaccine in late 2020, has now also given the first green light to a variant-adapted shot that targets both the original and Omicron version of the virus.
The UK medicines regulator (MHRA) gave the so-called bivalent vaccine made by U.S. drug company Moderna conditional approval as a booster for adults on Monday.
Later on Monday, the UK's Joint Committee on Vaccination and Immunisation (JCVI) backed the use of the variant-adapted shot in the country's booster campaign starting September.
The MHRA's Moderna decision was based on clinical trial data that showed the booster triggered "a strong immune response" against both Omicron (BA.1) and the original virus, it said.
Moderna in June said trial data showed that when given as a fourth dose, the variant-adapted shot raised virus-neutralizing antibodies by eight-fold against Omicron.
The MHRA also cited an exploratory analysis in which the shot was found to generate a "good immune response" against the currently dominant Omicron offshoots BA.4 and BA.5.
According to Moderna, trial data showed its variant-adapted booster generated virus-neutralizing antibody levels against the subvariants that were 1.69 times higher than those given the original booster.
However, the correlation between neutralizing antibody levels and vaccine effectiveness against disease - in particular severe disease - remains unclear.