Wherever I go, everyone says: tell us more about Omicron,” says Senjuti Sara, molecular microbiologist and director of the Child Health Research Foundation in Decca, Bangladesh. “There is so little understanding of what’s going on, and that’s true, even for scientists.”
Nature rounds up what scientists know so far about the Omicron variant.
How fast is Omicron spreading?
Omicron’s rapid rise in South Africa is what worries researchers most, because it suggests the variant could spark explosive increases in COVID-19 cases elsewhere. On 1 December, South Africa recorded 8,561 cases, up from the 3,402 reported on 26 November and several hundred per day in mid-November, with much of the growth occurring in Gating Province, home to Johannesburg.
Epidemiologists measure an epidemic’s growth using R, the average number of new cases spread by each infection. In late November, South Africa’s National Institute for Communicable Disease (NICU) in Johannesburg determined that R was above 2 in gating. That level of growth was last observed in the early days of the pandemic, Richard Lessens, an infectious-disease physician at Kabul- Natal University in Durban, South Africa, told a press briefing last week.
Gating’s R value was well below 1 in September — when Delta was the predominant variant and cases were falling — suggesting that Omicron has the potential to spread much faster and infect vastly more people than Delta, says Tom Senseless, an evolutionary biologist at KU-Leuven in Belgium. Based on the rise in COVID-19 cases and sequencing data, Senseless estimates that Omicron can infect 3 to 6 times as many people as Delta, over the same time period. “That’s a huge advantage for the virus — but not for us,” he adds.
Researchers will be watching how Omicron spreads in other parts of South Africa and globally to get a better read on its transmissibility, says Christian Althaus, a computational epidemiologist at the University of Bern, Switzerland. Heightened surveillance in South Africa could cause researchers to overestimate Omicron’s fast growth. But if this pattern is repeated in other countries, it’s very strong evidence that Omicron has a transmission advantage, adds Althaus. “If it doesn’t happen, for example, in European countries, it means things are a bit more complex and strongly depend on the immunological landscape. So we have to wait.”
Although genome sequencing is needed to confirm Omicron cases, some PCR tests can pick up a hallmark of the variant that distinguishes it from Delta. On the basis of this signal, there are preliminary signs that cases, Although extremely low, are rising in the United Kingdom. “That’s certainly not what we want to see right now and suggests that Omicron could indeed also have a transmission advantage in the UK,” Althaus adds.
Can Omicron overcome immunity from vaccines or infection?
The variant’s swift rise in South Africa hints that it has some capacity to overcome immunity. Around one-quarter of South Africans are fully vaccinated, and it’s likely that a large fraction of the population was infected with SARS-CoV-2 in earlier waves, says Senseless, based on heightened death rates since the start of the pandemic.
In this context, Omicron’s success in Southern Africa might be due largely to its capacity to infect people who recovered from cases of COVID-19 caused by Delta and other variants, as well as those who’ve been vaccinated. A 2 December preprint1 from researchers at the NICU found that reinfections in South Africa have increased, as Omicron has spread. “Unfortunately, this is the perfect environment for immune escape variants to develop,” says Althaus.
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