It is because “Omicron is spreading significantly faster than the Delta variant in countries with documented community transmission, with a doubling time between 1.5-3 days”, WHO said.
The WHO also noted it is uncertain whether the observed rapid growth rate can be attributed to immune evasion, intrinsic increased transmissibility or a combination of both.
Moreover, on severity of Omicron, the UN health body stated that the data is “still limited”.
However, hospitalisations in the UK and South Africa due to the variant continue to rise, and given rapidly increasing case counts, it is possible that many healthcare systems may become quickly overwhelmed.
Preliminary data suggest that there is a reduction in neutralising titres against Omicron in those who have received a primary vaccination series or in those who have had prior SARS-CoV-2 infection, which may suggest a level of immune evasion.
“There is still limited available data, and no peer-reviewed evidence, on vaccine efficacy or effectiveness to date for Omicron,” the WHO said.