Second Waves, Magic Thresholds
Let’s set aside the wave analogy. Michael T. Osterholm, the director of the Center for Infectious Disease Research and Policy at the University of Minnesota, says that it’s far more accurate to think of the pandemic as a forest fire. We have suppressed it in some places, but we have not put it out completely. “It’s going to keep burning as long as it has wood,” he says. “In this case, wood is humans that are susceptible to infection.”
It’s safe to assume that case counts will rise in the coming months, as colder weather forces more people indoors (in the North, at least) and as more students and teachers return to in-person schooling. Colleges are already grappling with outbreaks, and infected students are already returning home to seed a further spread in their own communities.
“Case counts could start spiking just a few weeks from now,” Peter Hotez, the dean of the National School of Tropical Medicine at the Baylor College of Medicine in Texas, told me. “The most rigorous predictions are that we head into November with 220,000 deaths.” And if pandemic-fatigued families travel to spend the holidays together, it will get worse in late fall and winter.
It’s tough to say whether the nation will reach or surpass the grim peaks of the summer, when we were seeing 65,000 to 70,000 new cases every day. Hopeful policymakers have speculated that fall outbreaks will be less severe, because many communities are at or approaching the herd immunity threshold — the point at which enough people have become immune to the virus that it can no longer spread easily. But there are several problems with this hypothesis.
First, we don’t really know how durable immunity to the virus might be. Most scientists think it’s likely that it lasts anywhere from several months to a year. But doctors have confirmed a few cases of repeat infection and, in at least one of them, the second infection proved more severe than the first.
Second, herd immunity is not a magical doorway that will take us back to the before-times. “People think once we hit this number we can all go to the bar because now it’s over,” Dr. Jha says. “But it doesn’t work like that.” It’s hard to know what the threshold even is (most experts put it at around 60 percent or higher, though some argue it could actually be much lower) and difficult to say when a population has crossed it. But even then, the virus would only slow down, not stop.
Third, most experts agree that, whatever the threshold proves to be, no country in the world is there yet. Even if some of the hardest hit communities — in Corona, Queens, for example — are partly protected, antibody tests indicate that, overall, just 10 percent to 12 percent of Americans have been infected with the virus to date. If SARS-CoV-2 is a forest fire, it still has a lot of wood to burn through.