Transmissibility, severity, reinfection of Omicron BA.2 subvariant

A more contagious subvariant of omicron, known as BA.2, is spreading across the globe and could soon become the dominant version of Covid-19.

It’s now the top variant in at least 18 countries and rapidly spreading, representing 35% of all new cases that have been genetically sequenced worldwide, up from ten countries and 21% of cases the week before, according to new data from the World Health Organization. In the U.S, BA.2 currently makes up 3.8% of genetically sequenced Covid cases, according to the Centers for Disease Control and Prevention.

A pandemic weary public wants to know two main things: Will BA.2 cause a second surge of omicron cases, and will it put even more people in the hospital with severe infections? So far, scientists say the answer to both questions is probably no.

However, Danish scientists confirmed this week that the new subvariant can reinfect people who’ve previously had omicron, although it doesn’t appear to be all that common. They also agree that it’s more contagious than the original version of omicron, BA.1, which is still widely circulating around the world.

But it’s surprisingly not driving a second wave of omicron infections. Globally, Covid cases have plunged 21% over the past week — subsiding in every region except the Western Pacific — while deaths have fallen 8% over the past week, according to data from the WHO.

Maria Van Kerkhove, the WHO’s Covid-19 technical lead, said the global health agency is closely monitoring countries that have detected BA.2, but so far the subvariant hasn’t caused a fresh surge in cases.

“As we’re seeing that decline in cases in countries, we’re not seeing an increase again with BA.2,” Van Kerkhove said during a question-and-answer session livestreamed on the WHO’s social media platforms Tuesday.

Here’s what’s known about the subvariant so far.

Danish researchers have found that BA.2 is about 30% more transmissible than BA.1. Denmark was one of the first countries where BA.2 became dominant, and public health authorities around the world have paid close attention to the situation there to gather insight on what the subvariant might mean for the future course of the pandemic.

“We conclude that Omicron BA.2 is inherently substantially more transmissible than BA.1,” a team of scientists affiliated with Danish public health authorities and the University of Copenhagen wrote in a study last month, which has not yet been peer reviewed.

The U.K. Health Security Agency found in late January that BA.2 had a substantial advantage over BA.1 in England. “We now know that BA.2 has an increased growth rate which can be seen in all regions in England,” said Dr. Susan Hopkins, the agency’s chief medical advisor.

“If what is being reported is true that BA.2 is slightly more transmissible, then my strong inclination is to say that BA.2 will likely take over wherever BA.1 was,” said Mehul Suthar, a virologist at Emory University.

However, Suthar…