• "There is a suggestion that there is increased transmissibility, what we need to understand is if it's more or less transmissible compared to delta," WHO official Maria Van Kerkhove said.
• Van Kerkove said there are increasing hospitalizations in South Africa, but public health officials haven't seen an increased risk of death yet, but they're waiting on more data.
• Dr. Mike Ryan, executive director of the WHO's health emergencies program, said public health officials initially saw mild cases with the alpha and delta variants as well.
• Ryan said “clearly the virus does appear to be transmitting efficiently.”

The World Health Organization on Friday said the Covid omicron variant has been detected in 38 countries, up from 23 two days ago, with early data suggesting the strain is more contagious than delta.

"We do see an increasing growth rate, we see increasing numbers of omicron being detected," Maria Van Kerkhove, the WHO's Covid-19 technical lead, said during a Q&A livestreamed on the group's social media channels Friday. "But we have reports of omicron in 38 countries in all six WHO regions."

"There is a suggestion that there is increased transmissibility, what we need to understand is if it's more or less transmissible compared to delta," Van Kerkhove said, noting that the delta variant is still dominant across the globe.

Dr. Mike Ryan, executive director of the WHO's health emergencies program, said "clearly the virus does appear to be transmitting efficiently."

"And we saw that before with delta. So again, there's certain things we shouldn't be surprised with," Ryan said. 

Omicron has some 30 mutations on the spike protein, which is the mechanism used to bind to human cells. Some of these mutations are associated with higher transmission and the ability to escape immune protection, according to the WHO.

South African scientists this week found that omicron is associated with a "substantial ability" to reinfect people who already had Covid, compared with past variants of the virus. The study, published by the South African Centre for Epidemiological Modelling and Analysis and the National Institute of Communicable Diseases, has not yet been peer reviewed.

Van Kerkhove said it's still too early to understand the severity of disease caused by omicron. Early reports of mild symptoms in some of the first cases where it was identified were based on a cluster of university students who tend to be younger and experience more mild symptoms than older adults, she said.

"There was initial reports that it tended to be more mild, but it's really too soon," Van Kerkhove said. "Everybody who is infected with SARS-CoV-2 regardless of what variant will always start out with a mild disease. And so maybe it will stop there with mild, some people are asymptomatic of course, but it may stop with mild disease or it may take some time."

Van Kerkove said there are increasing hospitalizations in South Africa, but public health officials haven't seen an increased risk of death yet, but they're waiting on more data.

Ryan said public health officials initially saw mild cases with the alpha and delta variants as well. It could take two weeks to see increased mortality associated with omicron if the variant does, in fact, cause more severe disease.

"It takes time unfortunately," Ryan said. "We saw that as well in previous waves of this pandemic. When the incidence rate goes up, it takes a week or two for that to result in hospital admissions and deaths."

Van Kerkhove cautioned there's a reporting bias at the moment which may obscure how virulent the variant really is. Many of the people around the world who have tested positive for omicron were healthy travelers, which could explain why the symptoms reported so far are mild.

"If you're traveling, you're not sick or you shouldn't be traveling if you're sick," Van Kerkhove said. "So there's a bias in terms of what is being detected at the moment, but that will change over time."

The first person in the U.S. who tested positive for omicron was a fully vaccinated traveler between 18 and 49 years of age returning from South Africa to the San Francisco area.

Van Kerkhove called on nations around the world to increase genetic sequencing of Covid-19 cases to detect new variants and share the results publicly to better understand the evolution of the virus.

"Now is the time to beef up the systems," she said. "You've heard us say that for quite some time now, but it's not too late to do this -- systems need to be reinforced."

Van Kerkhove noted that South Africa was the first country to report omicron to the WHO, but the timeline could change as more countries sequence a backlog of Covid cases from November.

"So some of the earliest cases of this particular variant may very well not be in South Africa," she said.

Van Kerkhove and Ryan said the current vaccines remain the most effective measure to slow transmission of the virus. Ryan said there's a "clear relationship" between vaccine inequity and the development of variants around the world. The WHO has repeatedly criticized wealthy nations for not doing enough to get vaccines to people in poorer countries.

Pfizer and Moderna have said it will take about two weeks to know how omicron impacts the current vaccines as researchers gather data.

"Right now there is no need to change the vaccines we're currently using," Ryan said. "There is no evidence to support that. There is no evidence there to change,  but there's a lot of work going on to look at if we were to change, how might we change those vaccines and that work needs to be done upfront."