In the race to protect their populations against the Omicron coronavirus variant, countries including the UK and US, are rolling out extensive booster programmes after data showed additional jabs provided more protection against the new strain than two shots.
The data — from the University of Oxford — on Monday showed levels of neutralising antibodies that attacked the virus fell against Omicron, compared with Delta, in people who had taken two doses of the vaccine it developed with AstraZeneca, or of the BioNTech/Pfizer shot.