Guest: Dr. Sumon Chakrabarti, infectious diseases physician at Trillium Health Partners in Mississauga

News and serious worry over the Omicron variant of COVID-19 spread almost as quickly as the virus itself. The World Health Organization says the newest, potentially more contagious variant poses a "very high" global risk. The UK's Health and Security Agency calls it "the most worrying we've ever seen." In the span of a week and a half, the Omicron variant has been detected in more than a dozen countries around the world. But what do we really know about Omicron? What makes it more transmissible? Given what we know about how COVID works, how worried should we be? Today on "This Matters," we go to the basics with an infectious diseases doctor to explain why scientists believe the variant is more transmissible, talk through what we know and perhaps more crucially, what we're still waiting to find out.