COVID Cases In The U.S. Are Declining. When Will We Get To Herd Immunity?

Photo: Alexi Rosenfeld/Getty Images.
Almost a year after the first reported cluster of COVID-19 cases in the U.S., there's finally a speck of hope. In some states, nearly 20% of people have received their first dose of the vaccine, and a third, single-shot vaccine could be approved by the end of this week. As of Friday, over 68 million doses of the vaccine have been administered nationwide. And cases are down, too: although they're still higher than they were over the summer, we're averaging around 69,000 new cases a day, compared to a January peak of 300,000. 
So, when will we reach herd immunity? Technically, experts say that to reach herd immunity, over 70% of a population must be vaccinated. As of Friday, 6.5% of Americans have received both vaccine doses, and 13.9% have received at least one shot. But projections in the U.S. are currently a little more complicated.
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"We all expect that this virus is not different from other viruses and that we will reach a point that a sufficient number of people are immune so that the virus cannot jump any more," Dr. Arturo Casadevall, Johns Hopkins University chair of molecular microbiology and immunology, told CNN. "It reaches a point that there are so few hosts, so few people that it can jump to, that the epidemic crashes. The number of cases is the threat, and in the declining curve, we see that the number of people it can jump to is dropping." 
The Biden Administration initially hoped to vaccinate 1 million Americans a day, but recently upped the goal to 1.5 million shots a day. According to Axios, in order to reach that 70% benchmark by Labor Day, the U.S. will need to administer 1.9 million shots a day; in order to reach that same percentage by January 1, 2022, we'd only need 1.2 million. The New York Times crunched some numbers using data from the Centers for Disease Control and Prevention, and at the rate we're going, 70% of the population should be vaccinated by November 11. 
Still, many moving and unknown factors could impact these projections. The New York Times also reported that, because a number of unvaccinated people are already immune due to prior infection, we could reach the 70% threshold by July. On this front, scientists are divided. Some have said that previously infected people should count towards herd immunity numbers because of low reinfection rates, while others have said that, to be safe, we should really only consider Americans who have received the vaccine. 
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A new shot could also speed up the process: Johnson & Johnson has said that, if the company's single-shot vaccine is approved, 20 million doses will be produced by the end of March, and 100 million doses will be produced by June. 
Currently, there are two major threats to herd immunity, and the first is complacency. Although COVID cases are decreasing, experts told Vox that easing restrictions could pose a serious threat and prolong the pandemic. Because of the decline in cases, many states are planning or already starting to lift restrictions: Massachusetts Governor Charlie Baker has said that he will reopen sports arenas at 12% capacity if cases continue to trend downward, and New York is reopening movie theaters at 25% capacity. "It seems we haven't yet learned the lessons of the pandemic, that if you start trying to return to 'normal' too soon, cases creep back up again," Tara Smith, a professor at the Kent State University College of Public Health, told Vox.
The other danger is the new, highly contagious variant B.1.1.7, and the possibility of other strains. As of Friday, at least 2,102 instances of the B.1.1.7 variant have been recorded in the U.S., with especially high numbers in Florida. The new strain — combined with Florida Gov. Ron DeSantis' notoriously nonexistent COVID regulations — could pose a serious problem.
Adam MacNeil, a CDC epidemiologist, said that the U.S. is "nowhere near" reaching herd immunity yet. "Currently we know that the majority of the U.S. population is not immune to SARS-CoV-2, and variants may cause this portion of the population that is not immune to increase," he said on Friday, adding that the only way to speed up the trajectory would be increased vaccination.
But there is hope that we will be in a significantly better place by this summer or fall, especially if we're able to vaccinate more people — and if Americans continue to wear masks and avoid large, indoor gatherings, which could become easier as the weather gets warmer. "The most encouraging thing to me is how rapidly that curve is coming down," Casadevall said. "It gives me hope that we're going to crash the curve before variants become a threat."

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