Preliminary evidence suggests there may be an increased risk of reinfection with Omicron (which means people who have previously had Covid-19 could become reinfected more easily with Omicron), as compared to other variants of concern, the World Health Organization said.

The Organization said information is still limited.

"WHO is working with technical partners to understand the potential impact of this variant on our existing countermeasures, including vaccines. Vaccines remain critical to reducing severe disease and death, including against the dominant circulating variant, Delta. Current vaccines remain effective against severe disease and death," WHO said.

"The widely used PCR tests continue to detect infection, including infection with Omicron, as we have seen with other variants as well. Studies are ongoing to determine whether there is any impact on other types of tests, including rapid antigen detection tests."