Early reports from South Africa seem to indicate the omicron variant of coronavirus is much more contagious than previous variants while causing milder disease, though experts there warn definitive data won’t be available for weeks.
“This virus comes with both barrels loaded – high infectivity and potentially the ability for immune evasion. But maybe what it’s lacking is pathogenicity,” said Dr. Warner Greene, director of the Center for HIV Cure Research at the Gladstone Institutes in San Francisco.
COVID-19 cases in South Africa’s Gauteng province are doubling every day and 75% of infections are due to omicron. There is also a week-over-week increase in hospital admissions.
But so far, there have not been an increase in deaths or even hospitalized people who require oxygen, said Greene, who spoke on a call with reporters Monday.
How does COVID-19 affect me? Don’t miss an update with the Coronavirus Watch newsletter
Currently, the global epicenter of omicron cases is the Tshwane district in  the Gauteng province to the northeast of Johannesburg. Cases there have increased exponentially in the past several weeks, according to the South African Medical Research Council.
There are now early clinical reports out of hospitals in Gauteng emerging, and they are encouraging, Greene said.
“This looks to be a highly infectious virus, but it may not be as virulent or as pathogenic as the delta variant,” he said. But more data is needed to make any firm conclusions. 
Even the feel of the hospitals is different this time, the research council’s Dr. Fareed Abdullah wrote in a post on Saturday.
In all three previous COVID-19 waves in the country, “the COVID ward was recognizable by the majority of patients being on some form of oxygen supplementation with the incessant sound of high flow nasal oxygen machines, or beeping ventilator alarms.”
Abdullah isn’t convinced it’s possible to know yet if omicron is milder by what’s being seen today. 
“This may be due to the usual lag between cases and deaths and the trend will become clearer over the next few weeks,” he wrote.
Omicron is the most recently discovered variant of the SARS-CoV-2 virus that causes COVID-19. It first was first detected in southern Africa and named a “variant of concern” by the World Health Organization on Nov. 26.
As of Monday, it has been detected in more than 38 countries and one-third of U.S. states.
USA TODAY
Omicron had more than 50 mutations and appears to be far more contagious than the delta variant.
How well a disease can spread is defined by its basic reproductive number, sometimes written Rt.
For measles, the number is 12 to 18, meaning each person with measles on average infects 12 to 18 other people. The number for COVID-19 was originally estimated to be between 1.4 and 2.4, according to the World Health Organization. 
The Rt for the omicron variant appears to be about 3.5, said Trevor Bedford, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle is tracking it. 
Where did the coronavirus omicron variant come from? Scientists suggest it evolved in one person.
“These are still very early estimates and all this will become more clear as we get comparable estimates from different geographies and with different methods,” Bedford tweeted, noting the data he used is from South Africa.
“Even Rt of 3 is very high,” he wrote. “I’m hoping that prior immunity protects against severe outcomes, but I’m very concerned about the size of the epidemic wave in the US and across the world.”
A paper published Thursday from data from South Africa’s National Notifiable Medical Conditions Surveillance System found that having been previously infected with COVID-19 was not as protective against omicron as it was with the beta and delta variants. 
The paper, which has not yet been peer-reviewed, looked at the risk of reinfection. The study estimated that omicron may be twice as likely to cause reinfection as previous variants.
‘It was just a matter of time’:How scientists in San Francisco found the first case of the omicron COVID-19 variant in the US
Overall, news of the variant’s transmissibility and virulence could be good news, with the understanding that certainty is weeks away, say experts.
“It would be a great thing if, in fact, omicron crowded out delta. If omicron was a less pathogenic virus, that would be very good news for the human race,” said Greene.
It also makes sense for the virus to evolve in the direction of being less dangerous, said Dr. Paul Offit, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia
“It’s never to the advantage of the virus to kill you,” he said. “All viruses want to be the common cold, just give you the sniffles while you go around infecting others.”

source