It got noticed because of a surge of cases in South Africa.

"This new variant, B.1.1.529 seems to spread very quick!" Tulio de Oliveira, director of South Africa's Center for Epidemic Response & Innovation, and a genetics researcher at Stellenbosch University, said on Twitter.

Also, genetic sequencing showed it carried a large number of troubling mutations on the spike protein -- the knoblike structure on the surface of the virus that it uses to grapple onto the cells it infects.

Some of those mutations were already recognized from other variants and were known to make them more dangerous, including one called E484K that can make the virus less recognizable to some antibodies -- immune system proteins that are a frontline defense against infection and that form the basis of monoclonal antibody treatments.

It also carries a mutation called N501Y, which gave both Alpha and Gamma their increased transmissibility.

Just last week, Scott Weaver of the University of Texas Medical Branch and colleagues reported in the journal Nature that this particular mutation made the virus better at replicating in the upper airway -- think in the nose and throat -- and likely makes it more likely to spread when people breathe, sneeze and cough.

Like Delta, Omicron also carries a mutation called D614G, which appears to help the virus better attach to the cells it infects.

"The number of mutations per se does not mean that the new variant will cause any problems; although it may make it more likely to look different to the immune system," Dr.

However, WHO says it's unlikely these mutations would affect other Covid-19 treatments, including antiviral drugs in development and the steroid dexamethasone.

So far, Omicron has been detected in a handful of countries, including South Africa and Botswana, and among travelers to Belgium, the Netherlands, Australia, the UK, Italy, Israel and Austria, according to the GISAID database, as well as Canada, according to officials.

It takes an extra layer of testing above and beyond standard tests to detect infection to tell which variant of coronavirus has infected someone.

And South Africa has many people infected with HIV -- which suppresses the immune system -- who are currently unable to get treatment, and who may be more susceptible to infection.

Those factors may influence the rise of the variant in South Africa as opposed to countries where more people are vaccinated and fewer have immunocompromising conditions.

Physical barriers also will work against any mutant virus.

It carries 23 mutations, including one called N501Y that increases transmission.

It's fully susceptible to monoclonal antibody treatments and vaccines.

Beta

First seen in South Africa, the B.1.351 or Beta variant has both the E484K mutation that is linked with immune escape and the N501Y mutation suspected of helping make many other variants more contagious.

It has been shown to be 50% more transmissible than older strains and evades Lilly's dual monoclonal antibody treatment, but not others.

Blood tests and real-life use both suggest it can infect people who have recovered from coronavirus and also people who have been vaccinated against Covid-19.

Vaccine makers trying to get out ahead of the new variants by developing booster shots had focused on B.1.351, as it's the variant scientists most fear could elude vaccine protection.

But partial escape doesn't mean full escape, and vaccines are still expected to protect people to some degree.

It was overtaken by Delta in South Africa and have never gained much of a foothold in the US, despite the worry it caused, and is now designated a Variant Being Monitored by the CDC.

Gamma

The P.1 or Gamma variant that swept Brazil also never gained much ground elsewhere and is also now a CDC Variant Being Monitored.

Gamma carries both the E484K and N501Y mutations, with more than 30 others.

It's now designated Variant Being Monitored by the CDC.

Variants Being Monitored by CDC

All of the following variants are listed by the CDC as Variants Being Monitored.