Omicron: What we know — and don't know — about the new COVID-19 variant

The Omicron variant of SARS-CoV-2 is the latest strain of the coronavirus to be designated a "variant of concern" by the World Health Organization: more and more countries are reporting cases, and it has an unusual combination of mutations that may enable it to spread faster. Scientists are also trying to determine whether the current vaccines are effective against it.

American health authorities say no cases have yet been reported here, but over the weekend, like several other countries, the Biden administration placed travel restrictions on several southern African countries where cases were first spotted.