Washington, Jan 7 (IANS): The efficacy of boosters against Covid-19 will likely decline over time, and people may need a fourth shot to increase their protection, Moderna CEO Stephane Bancel has said.

According to Bancel, people who received their boosters last year will likely have enough protection to get them through the winter, when new infections surge as people gather indoors to escape the cold.

However, he said that the efficacy of boosters will probably decline over the course of several months, similar to what happened with the first two doses, CNBC reported on Thursday.

"I will be surprised when we get that data in the coming weeks that it's holding nicely over time - I would expect that it's not going to hold great," Bancel was quoted as saying, referring to the strength of the booster shots.

However, Oxford vaccine expert Sir Andrew Pollard recently said that regular booster doses every four-six to fight Covid may not be a sustainable way to prevent Covid infections.

"Administering booster vaccines to everyone every six months was 'not sustainable'," Pollard was quoted as saying to the Daily Mail.

"We can't vaccinate the planet every four-six months. It's not sustainable or affordable. In the future, we need to target the vulnerable," said Pollard, who was chief investigator of the Oxford Covid vaccine trials and director of the Oxford Vaccine Group, which developed AstraZeneca's jab.

"Today, less than 10 per cent of people in low income families have even had their first dose, so the whole idea of fourth doses globally is just not sensible," Pollard was quoted as saying to Sky News.

According to Pollard, future immunisation drives should target the most vulnerable, rather than all adults.

In the wake of Omicron spreading rapidly around the globe, Israel has rolled out a fourth dose for over-60s, while health authorities in Germany, UK and France are planning a second booster.