The U.K. variant, which scientists call B.1.1.7, is “of grave concern,” he said: In every country it’s dominated, this variant has increased the disease’s reproduction number—R, a measure of how easily a disease spreads—by 50 percent. If R is higher than 1, then a surge is building. Right now, California has an R of 0.77, according to the Centre for the Mathematical Modelling of Infectious Diseases. Were B.1.1.7 to become the dominant strain in California right now, Andersen said, the state would head back into a surge.
“The U.S. has never been at an effective reproduction number that would allow us to control the variant,” he said.
Even aside from the variant, predicting the virus’s fate in the spring is hard. To understand why, we can look at the stars.
Not astrology: I mean literally looking at the stars. When you peer through a telescope at Proxima Centauri, the sun’s nearest neighbor, you never see the star as it exists today. Its light takes time—4.2 years—to reach us and register in a measurable way.
Try to determine what’s happening in the pandemic at any one moment—how many people are now infected with the virus, for instance—and you face the same problem. Pandemic data suffer a lag too, although biological math and human circumstance, not the vastness of space, determine their delay.
In practice, COVID-19 case and test data are a window to the recent past. On average, patients do not develop their first COVID-19 symptom until four or five days after exposure to the virus. Figure that it takes another day or two for someone to get tested, then another for the lab to run the test and deliver a result. The COVID Tracking Project at The Atlantic estimates that another one to three days elapse as the lab reports the result to the state and the state publishes it. This lengthy process means that someone who is reported to be sick today might have been infected a week or two ago.
This latency matters just as much when the pandemic news is good as when it’s bad—and in recent days, the news has been very good. In the past week, the average number of new cases a day has fallen by double-digit percentages in 38 states and by single-digit percentages in eight, according to data from the COVID Tracking Project. (Cases are rising by double-digit percentages only in Texas and Washington.) Hospitalizations are a more timely measure of the pandemic’s spread and they, too, are falling in every state but Vermont and New Mexico. Even former hot spots are abating: In California, the average number of new cases has fallen by more than half since January 1.
The speed of vaccinations is increasing. In the past week, the U.S. has given 1.3 million shots each day, according to Bloomberg, meeting President Joe Biden’s initial goal of vaccinating 1 million Americans a day. (Biden, in response, upped the goal to 1.5 million vaccinations a day.) Life’s daily rituals could begin to resume: As the Harvard epidemiologist Julia Marcus recently wrote in The Atlantic, if you get a vaccine, you should be able to hug another vaccinated person with much less apprehension. Although something could still go horrendously awry—a strain of the virus could evolve, for instance, against which the vaccine is dramatically less effective—that seems, for now, unlikely.