London, Jan 5 (IANS): Regular booster doses every four-six months to fight Covid may not be a sustainable way to prevent Covid infections, said Oxford vaccine expert Sir Andrew Pollard.

Amid rising cases due to Omicron, which has the potential to escape vaccine immunity, calls for booster jabs got supercharged with many countries including the US, UK and India rolling out a third dose.

"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.

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

"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.

"It may be that as science evolves we can work out who the most vulnerable are in populations and target future boosters for them to maintain their protection."

However, in the wake of Omicron spreading rapidly, Israel has rolled out a fourth dose for over-60s, while both German and British health officials are planning for a second booster.

Pollard advised that Britain shouldn't start rolling out fourth Covid vaccines until there is more evidence they are even needed, the report said.

While the UK has seen a significant surge in cases, infections are reportedly mild.

Pollard noted it is not clear why Omicron is causing more mild disease or that future versions of Covid will be similarly less severe.

Updated versions of Covid jabs may be needed to "manage living with the virus in the future", he said.

Vaccine makers are already working on tweaking the current crop of jabs in case they are needed against Omicron. But these won't be ready for months and so far the current vaccines are holding up against severe Covid outcomes.