The Omicron has overtaken Delta as the dominant strain in the US, many European countries, and the UK, and it is likely to become dominant in other countries soon.
Omicron is spreading faster than any known variant.
Barely one month after it was detected in South Africa, the highly contagious but less severe variant has spread to at least 110 countries.
The severity of Omicron has been topic of numerous debates in recent times.
However, scientists say Omicron appears to lead to fewer hospitalisations than Delta.
They argue that even if it is more transmissible than the Delta variant, it is not known just how much weaker it is.
Also, even as Omicron appears to lead to fewer hospitalisations than Delta, it is unknown whether it is causing fewer hospitalisations because the variant itself is less virulent.
The Omicron variant is spreading so fast, cases in some countries are doubling every two to three days.
A key unknown is whether Omicron will lead to increased hospitalisations, straining national health systems.
The World Health Organisation has stated that even if Omicron does cause less severe disease, the sheer number of cases could once again overwhelm unprepared health systems.
In South Africa hospitalisations appear to be limited, but experts note one reason could be the relative youth of its population compared to Europe.
Recent lab tests show that antibody levels in blood samples from people vaccinated with Pfizer-BioNTech and Moderna jabs drop when faced with Omicron.
The drop is even greater in those vaccinated with AstraZeneca or Sinovac, a Chinese jab authorised in about 50 countries.
A booster seems to increase antibodies, with both Pfizer and Moderna announcing positive results from recent tests.
But nobody knows how long the booster will be effective.
Even less is known about the efficacy of Novavax, the recently-approved vaccine because it was in clinical trials when the Alpha and Beta variants still dominated.
But this does not mean vaccines are useless against Omicron: the body has a secondary immune defence called T-cell response, which fights the virus by attacking infected cell
OMICRON overtakes Delta, more contagious, less severe