WHO experts warned Tuesday that repeating booster doses of the original Covid vaccines is not a viable strategy against emerging variants and called for new jabs that better protect against transmission.

An expert group created by the World Health Organization to assess the performance of Covid-19 vaccines said simply providing fresh jabs of existing Covid vaccines as new strains of the virus emerge was not the best way to fight the pandemic.

"A vaccination strategy based on repeated booster doses of the original vaccine composition is unlikely to be appropriate or sustainable," the WHO Technical Advisory Group on Covid-19 Vaccine Composition (TAG-Co-VAC) said in a statement.

It said preliminary data indicated the existing vaccines were less effective at preventing symptomatic Covid disease in people who have contracted the new Omicron variant, currently spreading like wildfire around the world.

But protection against severe disease, which is what the jabs were especially intended to do, "is more likely to be preserved".

It recommended developing vaccines that not only protect people against falling seriously ill but could also better prevent infection and transmission in the first place.

"Covid-19 vaccines that have high impact on prevention of infection and transmission, in addition to the prevention of severe disease and death, are needed and should be developed," TAG-Co-VAC said.

"Until such vaccines are available, and as the SARS-CoV-2 virus evolves, the composition of current Covid-19 vaccines may need to be updated, to ensure that (they) continue to provide WHO-recommended levels of protection against infection and disease by VOCs (variants of concern), including Omicron and future variants."