- Daily coronavirus cases in the United States have dropped by an average of 74% in the past six weeks.
- Experts are hopeful that the outbreak in the United States has overcome the situation.
- Economist Ian Shepherdson predicted the “effective end of the US COVID crisis” before May.
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As vaccinations against coronavirus increased in the United States earlier this year, hopeful progress has been overshadowed by fear of the variants. Scientists feared that B.1.1.7, the most contagious variant discovered in the UK, would keep coronavirus cases high during the winter, even when more people were vaccinated.
“The restrictions applied across the US now, on average, are not strict enough to control B.1.1.7,” wrote Ian Shepherdson, chief economist at Pantheon Macroeconomics, on February 12. He added that the US was “in a race between B.1.1.7 and the pace of vaccinations.”
But this week, Shepherdson changed his tone: “If the B.1.1.7 cases do not accelerate sharply next month, it will be realistic to call the effective end of the US COVID crisis – at least in terms of the case and hospitalization numbers – by late April, “Shepherdson wrote on Monday.
Daily cases in the United States have dropped by an average of 74% in the past six weeks. The country recorded less than 53,000 cases on Monday – its lowest daily count since October. On Tuesday, however, daily cases increased to almost 68,000.
Daily deaths have also decreased by 38% in the last six weeks, while daily hospitalizations have fallen by 55%.
“The balance is more optimism and less caution than it was four weeks ago,” Andrew Noymer, associate professor of public health at the University of California at Irvine, told Insider.
This sharp drop in infections and illnesses “was not necessarily predicted by people like me,” he added.
Many experts are now hopeful that the outbreak in the United States has changed the situation – at least in the coming months.
Why did cases drop so suddenly?
Diners sit outside at a restaurant in Alexandria, Virginia, on May 29, 2020.
REUTERS / Kevin Lamarque
Scientists don’t fully understand why cases have dropped so dramatically in the past six weeks.
Shepherdson suggested that B.1.1.7 may not be spreading as quickly as some epidemiologists feared.
“We still don’t see any signs that the spread of the more infectious variant B.1.1.7 is slowing the rate of decline, even in Florida, where it appears to be more prevalent,” he wrote.
Leana Wen, a visiting professor of health policy and management at George Washington University, told Insider that the main reason is probably that the holidays are behind us.
The United States was “at such a high before, with Thanksgiving and Christmas rising, that we’re finally falling for it,” she said.
Another factor that can contribute is that the decrease in tests means that fewer cases are being registered: the average of daily tests has decreased by 30% in the last six weeks. But that does not explain the considerable drop in hospitalizations and deaths.
The climate can also influence the dynamics of coronavirus outbreaks, as some studies have shown that warmer conditions can delay coronavirus transmission. But overall, the United States has seen no dramatic temperature changes from January to February.
“It’s probably a combination of things – a combination of having enough people who are already infected and people being vaccinated, so there is some level of protection,” said Wen.
This combination of natural and vaccine-derived immunity, some experts believe, may even be pushing the United States closer to a collective immunity limit.
Is the herd’s immunity closer than we think?
Alameda County officials line up for coronavirus vaccines outside St. Rose Hospital in Hayward, California, on January 8, 2021.
Jessica Christian / The San Francisco Chronicle / Getty Images
Most scientists do not believe that the United States has achieved collective immunity – the limit beyond which the virus can no longer spread easily from person to person. But some experts think we can be close.
Dr. Martin Makary, professor of surgery at the Johns Hopkins School of Medicine, wrote in The Wall Street Journal last week that “the consistent and rapid decline in daily cases since January 8 can be explained only by natural immunity.”
Based on that, he predicted that COVID-19 would be “virtually gone” in April.
Shepherdson suggested on Monday that the herd’s immunity “will not be far off” in April.
Scientists calculate collective immunity based on the reproductive value of a virus: the number of people infected by a patient, on average. Researchers generally estimate that the reproductive value of the coronavirus – the original virus, not a variant – is between 2 and 3, without interventions like vaccines or public health measures.
This means that about 50% to 67% of the US population would need to have some immunity – either through vaccination or natural infection – to obtain herd immunity.
But studies suggest that B.1.1.7 may increase the reproductive value of the virus by 0.4 to 0.9. In that case, the threshold for herd immunity would be higher: up to 75% of the US population would likely need to develop immunity.
“I don’t think there is any chance that we will be able to vaccinate 80% of Americans by July, so we will not achieve collective immunity until that point,” said Wen.
She added, however, that the United States is likely to see a “substantial decline” in infections until May, and a similar decline in hospitalizations in the deaths that will follow.
This period of lower infection rates, said Wen, “is our opportunity to get as much immunity in the community as possible” through vaccines.
Shepherdson hopes that as the United States approaches herd immunity, more companies will reopen.
“The gradual reopening of the service sector now underway will accelerate over the next two months,” he said, “with most of the economy open in plenty of time for Memorial Day.”
Andrew Dunn contributed reporting.