The World Health Organization says recent studies suggest a booster shot of the Pfizer-BioNTech vaccine could make it as effective against the Omicron variant as it is against Delta.

The UN health body released its latest technical brief for member states.

In the document, the WHO says preliminary findings from England indicate a significant reduction in vaccine effectiveness against symptomatic disease for Omicron compared with Delta after two doses of Pfizer-BioNTech or AstraZeneca vaccines.

It adds, however, there was higher effectiveness two weeks after a Pfizer-BioNTech booster, which was slightly lower or comparable to that against Delta.

The organization says available data are still limited and no peer-reviewed evidence on vaccine efficacy exist for the latest variant of concern.

The WHO says that as of Thursday, the variant was identified in 89 countries.

It says Omicron is spreading significantly faster than the Delta variant in countries with documented community transmission, with a doubling time between 1.5 to 3 days.

The WHO is calling on member states to increase testing and sequencing efforts to better understand circulating variants, including Omicron.