Geneva, December 20 (RHC)-- The World Health Organization (WHO) has admitted it doesn’t know why the Omicron variant is spreading so rapidly in countries with high levels of COVID-19 immunity.

In an update over the weekend, the WHO said Omicron had so far been reported in 89 countries and the number of cases was doubling in 1.5 to 3 days.  It said this was “significantly faster than Delta in countries with documented community transmission.”

However, the organization said it was unclear whether the new variant was spreading so fast among populations with high immunity due to its increased transmissibility, better immune evasion, or a combination of both factors.

"There are still limited available data, and no peer-reviewed evidence, on vaccine efficacy or effectiveness to date for Omicron,” the WHO said during a technical briefing, as quoted by Reuters.  It warned that given the speed of transmission and the growing number of hospitalizations in the UK and South Africa, “it is possible that many healthcare systems may become quickly overwhelmed.”

More data is also needed regarding the clinical severity of the variant, the WHO said, admitting it still does not understand “the severity profile and how severity is impacted by vaccination and pre-existing immunity."

Since its discovery in South Africa about five weeks ago, the rapid spread of Omicron has prompted fresh travel bans and new pandemic restrictions, with several countries announcing full-scale lockdowns. 

The UK has reported record daily numbers of new COVID cases for three days in a row, with more than 93,000 cases announced on Friday.  London authorities are reportedly mulling the idea of a new two-week strict lockdown after Christmas.