The World Health Organization warned on Friday that a new coronaviruses variant discovered in southern Africa was the most serious category the agency uses for such tracking.
The designation was announced after an emergency meeting of the health body. Delta, the last variant to receive this label, took off this summer and now accounts for most of the Covid cases in the United States.
The W.H.O. said the new version has a number of genetic changes that may allow it to spread quickly.
It would take more research to determine the extent of the threat, but independent scientists agreed that Omicron deserved urgent attention. Delta has lived up to initial worries, but others have had a limited impact.
William Hanage is an epidemiologist at the Harvard T.H. Chan School of Public Health. This could be bad. This could be very bad. We don't know enough to roll that tape forward.
Dr. Hanage said that vaccines will most likely protect against Omicron, but further studies are needed to determine how much of the shots effectiveness may be reduced.
There are new coronaviruses every now and then. The virus has no new advantage. The World Health Organization uses Greek letters to name the variants. The first variant of concern, Alpha, appeared in Britain in late 2020.
The genes of coronaviruses from positive test samples were sequenced at the Gaborone Harvard H.I.V. Reference Laboratory. Some samples shared about 50 different genes not found before. According to an international database of variant, six people have tested positive for Omicron in Botswana.
Researchers in South Africa stumbled across Omicron in a cluster of cases. There are 58 Omicron samples listed on the variant database. The director of the Centre for Epidemic Response & Innovation in South Africa said at a news conference on Thursday that close to two or three hundred Omicron cases would be released in the next few days.
The W.H.O. called for more research into its biology.
At the news conference, Dr. de Oliveira said that the variant did surprise them. The full significance is still uncertain.
The W.H.O. was asked to hold an emergency meeting on Friday by Dr. de Oliveira and his colleagues because of the spread of the Omicron variant in South Africa.
The researchers found a lot of changes on the surface of the coronaviruses. The immune system produces antibodies to fight a Covid-19 infection that targets the spike protein. Concerns were raised that Omicron's spike could be able to evade vaccine or previous infections.
Dr. de Oliveira and his colleagues decided how quickly Omicron was spreading in South Africa. The scientists figured out how to identify Omicron with a standard nasal swab test, despite the fact that it takes a long time to sequence the entire genome of a virus.
The tests are fast because they only look for two of the coronaviruses 29 genes. Omicron does not test positive for the spike gene because of its new mutations. Researchers could simply look for samples that tested positive for the same thing.
The spike-negative samples were surging across South Africa, suggesting that Omicron had a competitive advantage over Delta, which had been the dominant variant in the country.
Richard Lessells, an infectious disease specialist at the University of KwaZulu-Natal in South Africa, said at Thursday's news conference that it gives them concern that this variant may already be circulating in the country.
South Africa, where less than 25% of the population is fully vaccined, could see a surge of hospitalizations if Omicron is allowed to spread further. He said that they would like to be wrong on some predictions.
Europe, the United States and Canada have all banned flights from South Africa. Omicron has been seen in Hong Kong and Belgium, and may be in other countries as well.
Theodora Hatziioannou, a researcher at Rockefeller University in New York, said that Omicron's distinctive mutations raise the possibility that it first evolved inside the body of someone with H.I.V., whose immune systems may have been too weak to quickly fight it Dr. Hatziioannou said that your responses were not as good.
The virus may have lingered in that person for months, spending time gaining the ability to evade the immune system. Dr. Hatziioannou said that the virus has seen a lot of resistance.
The lab of Dr. Hatziioannou and her colleagues has been able to make viruses resistant to Covid-19. She said that Omicron has many different variations of the same regions. She said the overlap is striking.
Dr. Hatziioannou is concerned that Omicron will be able to evade some of the antibodies that people have acquired from vaccines or Covid-19 infections. She predicted that some treatments wouldn't work against Omicron because the variant's spikeProtein is protected from them.
Vaccines are expected to provide some protection against Omicron because they are stimulators of immune cells that can attack other cells, according to Dr. Hatziioannou. The immune-cell response is unaffected by the spike protein changes.
Booster shots could allow people to fight against new versions of Omicron. She said that the studies are only now ongoing.
There is no evidence that Omicron causes more severe disease. It is not clear how quickly Omicron can spread.
The earlier variant, such as Mu, had a strong ability to evade immune defenses. They were poor at transmitting and never became a serious threat to the world.
Some Omicron genes suggest that it may transmit well. The furin cleavage site is known to help the spike protein attach more effectively to cells, and three changes to the region are known to change that.
Dr. Hanage said he was not sure if the data from South Africa was accurate. He said it was too early to be definitive.
Even though the overall rate of daily new infections in the country remains very low, he was not sure how a variant could sweep so quickly across South Africa. He thought that early tests might have been hampered by a technical flaw that could be found in the next few days. He said it felt like part of the puzzle was missing.
It is possible that the spread of Omicron was just a coincidence. If a new variant gets swept along during a surge of cases, it will look very infectious.
Dr. Hanage thought a travel ban would be a good idea to give governments time to plan for dealing with Omicron if it goes awry. Health leaders could use the delay to put in stronger measures for preventing transmission or boosting vaccinations. He said that just doing it and thinking it will be enough is not a long-term plan.
Dr. Hanage said that vaccines would be vital in the fight against Omicron, both by slowing down its spread and making it more likely that people who do get sick only have mild Covid-19 instead of needing to go to the hospital.
Omicron is enough to be taken seriously, but not apocalyptic. It is not a magic virus. Magic viruses are not a thing.
