An expert body of the World Health Organization (WHO) warned Tuesday that repeating booster doses of the original COVID-19 vaccines is not a viable strategy against emerging variants and current jabs may need to be reworked to ensure efficacy against those variants, including omicron.

The technical group, made up of independent experts, said it would consider a change in vaccination composition and stressed that shots needed to be more effective in protecting against infection.

"The composition of current COVID-19 vaccines may need to be updated to ensure that COVID-19 vaccines continue to provide WHO-recommended levels of protection against infection and disease by VOCs (variants of concern), including omicron and future variants," the technical body, tasked with making recommendations to the WHO, said in a statement.

"COVID-19 vaccines need to ... elicit immune responses that are broad, strong, and long-lasting in order to reduce the need for successive booster doses," it added.

"A vaccination strategy based on repeated booster doses of the original vaccine composition is unlikely to be appropriate or sustainable."

However, the statement stopped short of advocating an omicron-specific vaccine at this stage, saying more research was required and urging manufacturers to share data.

It said that an updated vaccine could be aimed specifically at the dominant variant, which is currently omicron in many places, or be a "multivalent vaccine" designed to bust several variants at once. Further recommendations will be issued when more data is available, it added.

Some vaccine makers are already developing next-generation vaccines targeting omicron, the highly contagious variant first detected in southern Africa and Hong Kong.

On Monday, Pfizer Chief Executive Albert Bourla said a redesigned COVID-19 vaccine that specifically targets the omicron variant would probably be needed and his company could have one ready to launch by March.

Rival manufacturer Moderna Inc. is also working on a vaccine candidate tailored to omicron, but it is unlikely to be available in the next two months.

A WHO official had previously said the issue of vaccine composition required "global coordination" and should not be left to manufacturers to decide alone.