After weeks in free fall, new Covid-19 cases are starting to level off in the US, as the BA.2 subvariant continues its ascent.
BA.2 caused about 35% of cases in the US last week, up from 22% the week before, according to new estimates from the United States Centers for Disease Control and Prevention, which were posted on Tuesday.
“I would not be surprised at all if we do see somewhat of an uptick,” Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said in a live interview on Tuesday with the. “I don’t really see, unless something changes dramatically, that there will be a major surge,” he said.
It is more contagious than Omicron’s BA.1, which was already an extremely contagious virus with a basic reproduction number, or R-naught, of about 8, according to William Hanage, an epidemiologist at Harvard’s T.H. Chan School of Public Health, which means that a single infected person could be expected to transmit the disease to an average of 8 others.
Hanage says that at a population level, Omicron is much more manageable than Delta was, but it is not harmless. But the UK has its own challenges, too, says Dr. Carlos Del Rio, an infectious disease specialist and executive associated dean at the Emory School of Medicine. “They have a much, much older population than we do,” he says.
“And between the number of people infected and the number of people who were already vaccinated, we estimate that about 73% to 75% of the population has some degree of immunity,” he says.