• WHO said new Covid-19 cases in South Africa increased sharply over the last week amid the spread of the omicron variant, the dominant strain circulating in the country.
• During the week of Nov. 29 to Dec. 5, the country's cases increased by 111% from the previous week.
• South Africa's test positivity rate also hit 22.4% at the beginning of the last week, a sharp increase from 1.2% reported during the first week of November.

The World Health Organization said new Covid-19 cases in South Africa more than doubled over the last week amid the spread of the omicron variant, the dominant strain circulating in the country.

During the week of Nov. 29 to Dec. 5, South Africa's cases increased by 111% from the previous week, the WHO noted in a report released Wednesday. Roughly 62,000 new cases were reported in the country during the last week alone.

The percentage of positive Covid tests are also soaring with almost a quarter, 22.4%, of tests coming back positive at the beginning of last week, a significant increase from the 1.2% positivity rate reported during the first week of November, the WHO added in the report. 

But the exact cause of these increases is still unclear, WHO said. The agency said it is "plausible" that it was driven by the spread of omicron in combination with scaled back public health protocols and "sub-optimal" Covid vaccination coverage in the country. To date, 25.2% of the total population in South Africa is fully vaccinated, according to the WHO. 

The data comes as the omicron variant spreads across the world with confirmed cases in 57 countries. South Africa and Botswana, which both detected the variant early on last month, account for 62% of omicron cases reported as of Dec. 2, a separate WHO report released Wednesday said.

Meanwhile, scientists across the world are scrambling to answer questions about the new variant's transmissibility and severity.

Omicron has more than 30 mutations to the spike protein, which the virus uses to invade human cells. Some mutations affect the variant's virulence and indicate it could be more infectious than previous Covid strains, according to the WHO. 

On Wednesday, WHO Covid-19 technical lead Maria Van Kerkhove said preliminary evidence from South Africa may suggest the new variant is milder than the delta strain of Covid-19 but it is "too early to conclude on that." 

South African patients with a more mild course of the disease may not have gone through the full course of the infection, she said. Van Kerkhove also noted the evidence is largely based on anecdotal information rather than comprehensive studies. 

"It's too early to tell," Van Kerkhove said during the briefing. "I just only wanted to caution against any conclusions about the severity of omicron yet." 

But she said that vulnerable populations, such as individuals who are older, unvaccinated or have underlying conditions, have a considerably higher risk of developing severe disease.

Questions about the new variant's affect on vaccine efficacy remain unanswered as well, though new evidence emerged from a preliminary study released Tuesday by South African scientists.

The study found the variant significantly reduces antibody protection generated by Pfizer and BioNTech's vaccine. However, the South African scientists noted the patients who recovered from the virus and received a booster shot will likely have more protection from severe disease. 

At the Wednesday briefing, WHO Chief Scientist Soumya Swaminathan said it is still premature to conclude this "reduction neutralizing activity would result in a significant reduction" in vaccine efficacy. 

"We do not know that because as you know, the immune system is much more complex," Swaminathan said. "There are T cells, there are memory B cells, and so what we really need now is a coordinated research effort and not jumping to conclusions on you know, study by study."