A technical advisory group established by the World Health Organization said on Tuesday that current Covid-19 vaccines may need to be updated to ensure they are effective against new variants like Omicron.

"...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, including Omicron and future variants," the body of independent experts said in a statement sent to journalists by the WHO.

The WHO body said it will consider a change in vaccine composition to ensure vaccines protect against severe disease.

"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 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.