The United States has seen a dramatic drop in the number of Covid-19 cases and hospitalizations in recent weeks, a trend that epidemiologists see as an encouraging sign that the Delta wave of the virus has peaked nationally.
The seven-day average of daily new cases in America dropped from about 151,000 on 14 September to about 106,000 on 29 September, a 29% decrease, according to data from the Centers for Disease Control and Prevention.
The number of people admitted to the hospital with Covid-19, who at the peak of the Delta surge filled some intensive care units to capacity, has followed a similar downward trajectory in recent weeks.
Still, while those experts said they do not expect another surge as big as previous ones during the pandemic, they emphasized the virus remains a significant threat due to the large number of people who have not been vaccinated and the risk of a new variant, possibly even emerging from the unvaccinated population.
“Will the next surges be as big as this current one? It’s not likely, but it’s possible,” said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. “When you have 70 million people left who have not been vaccinated, many of whom have not yet been infected, that’s a lot of human wood for this coronavirus human forest fire to burn.”
America’s vaccination rate has slowed at a rate below many of its industrialized peers where the vaccine is widely available. Reasons vary, but are a mix of rightwing and religious opposition and skepticism, fears over safety, and concerns from communities of color wary of previous racist treatment by American healthcare institutions.
The downward trend can be attributed to increased immunity in the US population because of vaccination or natural infection and because of behavior change, such as people again wearing masks and avoiding travel or the large gatherings that they participated in before the recent surge, said Jennifer Nuzzo, an epidemiologist at Johns Hopkins University.
“We saw that as we relaxed everything at the end of June and July, then we saw another surge, partially attributable to Delta but also behaviors changed, and people went back to living in pre-Covid ways,” said Nuzzo.
Still, while there has been relief across much of the country, seven states have seen at least a 14% increase in Covid-19 cases over the last two weeks, according to data compiled by the New York Times.
That includes Maine and North Dakota, which have seen 29% and 25% increases during that period. The hardest hit appears to be Alaska, which has experienced a 75% increase in cases. Two of its hospitals have had to start rationing care, the Associated Press reported.
Bill Hanage, an epidemiologist at the Harvard TH Chan School of Public Health, said this year was following a similar trend to last fall, when Covid-19 surged through the south and then through more sparsely populated parts of the country.
“The difference this year is that spread is going to be impeded – or not – by vaccination,” said Hanage.
Ali H Mokdad, professor of health metrics sciences at the University of Washington, projects that the number of cases will eventually start to go up again in winter because of the unvaccinated, seasonality – with the weather getting colder and people gathering indoors rather than outdoors – and waning immunity among those who are vaccinated.
The size of that increase could be determined by whether more people get vaccinated – though that rate has largely plateaued – and by how people behave during Thanksgiving and Christmas.
“If Americans wear masks, we will not see a surge this winter,” said Mokdad. “So basically if we all take the vaccine and wear a mask, we could have a very close to normal winter.”
There is also an ongoing worry about a variant emerging that can evade the vaccines, Mokdad said.
Still, he and the other epidemiologists do not expect that we will again see a surge like August, when more than 100,000 people were hospitalized across the country.
“Mortality could start going up, but it will never reach the level that we had seen during the summer surge or during the last winter surge because the vaccines have been effective in preventing hospitalizations and deaths,” said Mokdad.
Despite that promising assessment, the virus experts were not ready to make predictions as to when life will return to normal.
“It’s not really fully answerable by science. It’s also about people’s comfort,” said Nuzzo, the Johns Hopkins epidemiologist. “One of the challenges for me in sorting through all this data is I actually don’t know what the off ramps are” from Covid precautions. “We haven’t defined that as a country.”
Osterholm, the University of Minnesota epidemiologist, thinks that “people are feeling like this is the end, [but] we’re vaccinating very few people for the first dose,” he said. “There will be more to come.”