The Omicron variant of Covid-19 appears to spread faster than the Delta strain and preliminary findings suggest that it reduces the efficacy of vaccines, the World Health Organization said on Sunday.

The global health agency, in its technical brief, added that Omicron seems to have a “growth advantage” over Delta, based on limited evidence available presently. The Delta variant was first identified in India earlier this year and accounts for over 99% of Covid-19 cases globally.

“It [Omicron] is spreading faster than the Delta variant in South Africa where Delta circulation was low, but also appears to spread more quickly than the Delta variant in other countries where the incidence of Delta is high, such as in the United Kingdom,” the World Health Organization said.

However, it is uncertain if the rapid growth of Omicron in countries with high levels of population immunity is related to immune evasion, increased transmissibility or both, it added.
“Given the current available data, it is likely that Omicron will outpace the Delta variant where community transmission occurs,” the World Health Organization said.

The public health agency added that limited data is available for how effective vaccines are against the Omicron variant. It said that there is no peer-reviewed evidence on this.

“Preliminary evidence, and the considerably altered antigenic profile of the Omicron spike protein, suggests a reduction in vaccine efficacy against infection and transmission associated with Omicron,” the World Health Organization said.

It added that there is some preliminary evidence to show that the occurrence of reinfection has increased in South Africa, where the Omicron variant was first identified in November.

Also read: How well prepared is India to detect the spread of Omicron?

“In addition, preliminary evidence from a few studies of limited sample size have shown that sera [fluid and solute component of blood] obtained from vaccinated and previously infected individuals had lower neutralisation activity [the size of the reduction ranges considerably] than with any other circulating VOCs [variants of concern] of SARS-CoV-2 and the ancestral strain,” it said.

The Omicron variant seems to be less severe than Delta, the World Health Organization said, citing preliminary findings from South Africa. “All cases reported in the EU [European Union]/EEA [European Economic Area] to date have been mild or asymptomatic,” it added.

However, more data is needed to understand the severity of Omicron, the global health body said.

On Thursday, the World Health Organization had said that according to preliminary data, hospitalisations across South Africa because of the Omicron variant remained low.

The Omicron variant has been detected in 63 countries as of December 9, according to the World Health Organization. India has confirmed 38 cases of the new strain so far in Maharashtra, Rajasthan, Delhi, Gujarat, Karnataka, Andhra Pradesh, Kerala and Chandigarh. All cases in the country are either asymptomatic or mildly symptomatic infections.

Concerns that the Omicron variant spreads rapidly has forced countries to introduce tougher travel rules for international passengers. India has stepped up monitoring of passengers from South Africa and several other “at-risk” countries.