This is what researchers know about how Omicron works.

The New York Times, December 19, 2021 (with Andrew Jacobs)

First identified in Botswana and South Africa in November, the Omicron variant has surged around the world over the past few weeks, faster than any previously known form of the coronavirus. While there’s a lot that scientists have yet to understand about Omicron, what they know already makes it clear that the variant could cause a huge number of new cases and that it could push some hospital systems to the breaking point.

Scientists first recognized Omicron thanks to its distinctive combination of more than 50 mutations. Some of them were carried by earlier variants such as Alpha and Beta, and previous experiments had demonstrated that they could enable a coronavirus to spread quickly. Other mutations were known to help coronaviruses evade antibodies produced by vaccines.

The first clues that Omicron could evade immunity came from South Africa, where scientists estimate that at least 70 percent of people have had Covid-19 at some point in the pandemic. An unexpectedly large fraction of Omicron cases involved people who had previously been infected.

When Omicron surged in England, British researchers similarly found that many people infected with the new variant had already survived Covid. The researchers estimated that the risk of reinfection with Omicron was about five times that of other variants.

For a deeper understanding of this increased risk of reinfection, a number of teams of scientists have studied the antibodies produced by people who recover from Covid-19. If they mix those antibodies in a dish with other variants, the antibodies do a good job of preventing the viruses from infecting human cells.

But if they mix those antibodies with Omicron, it still manages to get inside the cells much of the time. That means that the mutations Omicron carries are changing the shape of its surface proteins, where antibodies lock onto the coronavirus.

This ability to evade immune defenses is probably part of the explanation as to why Omicron cases are doubling so quickly — in some places, that can happen in as little as two days, or less.

While other variants are getting knocked out by antibodies, Omicron is succeeding in infecting more cells — making it more successful at getting into more people.