As of Thursday, there were 8,337 known cases of the B.1.1.7 variant in the country, but the actual number is probably much higher because labs in the country analyze only a very small proportion of the diagnosed cases. Still, the trend is clear: The variant — which is more transmissible and possibly more lethal — has been rising exponentially in the United States, its growth masked by the overall drop in infections.
“It is remarkable how much this recalls the situation last year where we had introductions of virus to different places that scientists warned would be a problem,” said Bill Hanage, an epidemiologist at the Harvard T.H. School of Public Health, said in an interview on Sunday. “People waited for them to be a problem before they took action — and then too late, they took action.”
Dr. Hanage said he was particularly worried about B.1.1.7 because it is at least 50 percent more transmissible than the original virus. The brisk pace of vaccinations will stem the tide somewhat, but the rising immunity in the population may be more than offset by the variant’s contagiousness, he added. “B.1.1.7 is really scary,” he said.
The vaccines in use in the United States — made by Pfizer-BioNTech, Moderna, and Johnson & Johnson — are expected to prevent severe disease and death from any of the variants, although they are slightly less effective against a variant that was identified in South Africa. That variant, known as B.1.351, has not yet spread widely in the United States.
Because many of the highest risk people have been inoculated, hospitalizations and deaths may not show a steep rise along with infections. But a surge in cases will still lead to some severe cases and deaths, Dr. Hanage said.