Dr Michelle Groome, of South Africa's Institue for Communicable Diseases (NICD), said omicron, which is feared to be more transmissible than the delta variant, is spreading at a “worrying” level.
Her comments came as South Africa, where omicron was first detected, recorded a further 8,561 cases of Covid on 1 December – up from 4,373 the previous day.
South Africa now has a seven-day average rate of 2,756 new infections, up from less than 300 on 16 November, according to Our World in Data. It is not yet known exactly how many of those cases were the omicron variant.
The rise in cases appears to be steeper and quicker than previous surges recorded in the country, though hospitalisations appear to be tracking previous climbs.
Gauteng province, which is at the heart of the omicron outbreak, recorded 580 hospitalisations this week – a jump of 330 per cent from 135 admissions two week ago, according to official data.
There has also been a 10 per cent spike in hospital admission of toddlers in the Tshwane area in South Africa, the NICD said.
The overall number of people with Covid-19 infections admitted to the hospitals in the past two weeks are in line with trends seen during the other waves of infections in the country, which were driven by delta and other variants, said Dr Waasila Jassat, a spokesperson at the NICD.
It remains unclear whether omicron causes more severe or milder disease in patients. The NICD said early data suggest that the variant, which has double the number of mutations found on its spike protein than delta, is able to evade some immunity.
A microbiologist at the NICD said on Thursday that there had been a rise in Covid patients contracting omicron in a way that did not happen with other variants.
“Previous infection used to protect against delta but now with omicron that doesn’t seem to be the case,” said Professor Anne von Gottberg during an online briefing organised by the World Health Organisation.
However, she said scientists believe symptoms are less severe for those reinfected with Covid by the new variant or infected after vaccination.
Current vaccines should still offer some protection against severe disease and death in patients with the omicron variant, although hospitalisations – the key metric driving decision making in governments around the world – are expected to rise.
The new variant has been detected in five out of nine South African provinces and was likely to be present all over the country, the latest official report on Wednesday said.
Omicron accounted for 74 per cent of the 249 virus genomes sequenced in South Africa in November, according to the NICD, which is collecting data as part of a wider national network for genomic surveillance.
South Africa conducts genome sequencing on only a small proportion of total samples collected each week. The NICD did not give a total number of confirmed cases of omicron infection.
"(The) mutation profile and epidemiological picture suggests omicron is able to get around some of our immune protection (to cause infection) but the protection against severe disease and death from vaccines should be less affected," the latest report from the surveillance network said.
The earliest sample in which the variant was detected was collected on 8 November in Gauteng, South Africa's most populous province, where Johannesburg and Pretoria are located.
Since then, it has been detected in Eastern Cape, Kwazulu Natal, Mpumalanga and Western Cape, and has spread to much of Europe, including the UK, where more than 30 cases of the variant have been recorded so far, as well as the United States and South Korea.
Earlier on Thursday, France and Greece recorded their first omicron cases.
In France, the infection was detected near Paris in a person who returned from Nigeria, the health body for the Ile de France region of greater Paris said in a statement.
Meanwhile, on Thursday, Germany imposed new restrictions on the unvaccinated as it seeks to break a dramatic surge in daily coronavirus infections exacerbated by the discovery of omicron.
Outgoing chancellor Angela Merkel and her successor, Olaf Scholz, reached an agreement with leaders of Germany's 16 states to restrict the unvaccinated from access to all but the most essential businesses, such as grocery stores, pharmacies and bakeries.
Additional reporting by agencies
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