Is the United States past the worst of the pandemic? Cases and hospitalizations have fallen in most states in the past few days, and vaccination news has brightened. Johnson & Johnson published trial data showing that its one-dose vaccine is safe and effective, and the Biden administration has bought 200 million additional vaccine doses from Pfizer/BioNTech and Moderna, which already have approved vaccines. By the start of the next school year, every American adult who wants a vaccine should be able to get one. The data scientist Youyang Gu, whose pandemic models have been justly celebrated for their performance, projects that the U.S. will reach herd immunity in late July.
The promise of summer vaccinations means that Americans can confidently plan for the end of the pandemic. The crisis is softening now, and America could crush it by autumn. What happens in between? The pandemic’s medium-term future remains the biggest outstanding question: March to May is the mystery.
The outlook is not all rosy. A consensus is developing that this window may be large enough to allow for another surge in cases, Kristian Andersen, an immunology professor at the private medical institute Scripps Research, told me. In fact, he expects such a surge, he said: The increased transmissibility of the U.K. variant makes any other outcome “unrealistic.”
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.
At the same time, the more transmissible B.1.1.7 strain of the virus is becoming more prevalent in the U.S.; early evidence suggests that it may harm young people and women more than the dominant coronavirus strains do. The strain will eventually dominate the U.S., Andersen told me: “It’s not an if; it’s a when,” Andersen said. He believes that it could become the principal strain in some areas by the end of this month. I wrote last week that the U.S. is now in a race of “vaccination versus variants”: It must confer immunity through vaccination faster than more virulent strains can cause another surge. Andersen had little doubt about who was currently winning that sprint. “The virus is moving faster than the vaccines right now,” he said.
This threat, along with the ambiguity about when vaccinations will become widely available, is what makes our fate in early spring unclear. The CDC estimated last month that the U.K. variant will not become America’s dominant strain until March.
Even if the U.K. variant (or another strain) does set off another explosion of infection, vaccines will stave off some of the destruction wrought by earlier surges. Deaths among nursing-home and long-term-care-facility residents make up at least 36 percent of all COVID-19 deaths in the U.S., according to COVID Tracking Project, but we know that the tally is incomplete; long-term-care facilities may account for as many as half of all deaths. By March, most long-term-care residents should be vaccinated, and many will have some form of protective immunity. Even if the U.K. strain induces a terrible run of cases, it might not cause as many hospitalizations and deaths. (But, Andersen cautioned, we are not on track to vaccinate everyone with comorbidities that quickly.)
Which brings us back to Proxima Centauri. Pandemic data lag, in part, because of the built-in biological delays. It takes time for someone to become infectious upon contracting COVID-19; it takes even longer for a region to boil over with cases. In Los Angeles County, one of the epicenters of the winter surge, cases started to rise on October 21, but they did so only modestly for five weeks before they seemingly exploded on December 1. Cases started to fall again seven weeks later.
Now look at the months to come: Within six weeks, the weather will have improved across large parts of the country. Families will be able to congregate outside again, lessening the temptation of riskier indoor gatherings. The days will lengthen everywhere, meaning that more of the sun’s virus-killing UV rays will reach the Earth’s surface. Most important, more and more Americans will get vaccinated, depriving the virus of susceptible victims.
Which isn’t to say that we’re in the clear: Although the viral trends are encouraging, the level of virus in the country remains horrifying. In many parts of the country, you are more likely to get infected with the virus today than you were during much of last year. “With viruses, what really matters is the population, not the individual,” Andersen said. There is still time for another deadly surge, especially one caused by a more transmissible and more lethal variant of the virus. But—and it’s a crucial but—there just isn’t much time.
Let’s say that, in a few regions of the country, cases begin to pick up again in the final week of February. Given how other surges have played out, we would normally expect cases to steadily grow for about five weeks before exploding—but since variants are now more transmissible, let’s say that the virus will explode after only three weeks of steady growth. Even then, according to Gu’s projections, the surge would take off within weeks of a key threshold, when one half of Americans have immunity to the virus either through vaccination or exposure—and right as the vernal equinox extends daylight hours everywhere.
So yes, it’s possible to imagine another costly surge of infection. The virus has subtle politics, you might say: It has consistently bamboozled experts so far, and it could do so again. But very large pandemic surges take time to develop—and time is the one thing that the virus, at long last, does not have on its side.