• The U.S. is headed for a new phase of the coronavirus pandemic as temperatures drop, flu season approaches and new cases of Covid-19 plateau at dangerously high levels.
  • Labor Day this weekend is among one of the first challenges of the fall for Americans.
  • Epidemiologists are concerned it might set the stage for another surge in cases — similar to the jump in U.S. cases following Memorial Day and the July 4 holidays.

The United States is headed for a new phase of the coronavirus pandemic as the country nears the fall, temperatures drop, flu season approaches and new cases of Covid-19 appear to plateau at a dangerously high level.

Labor Day this weekend is among one of the first challenges of the fall for Americans. Epidemiologists are concerned it might set the stage for another surge in cases — similar to the jump in U.S. cases following Memorial Day and Fourth of July holidays. The nation is heading into the holiday weekend with roughly 40,000 new Covid-19 cases a day, twice the number of daily cases from last spring, and with more businesses, events and activities reopened than before.

"We don't want to see a repeat of the surges that we have seen following other holiday weekends," White House coronavirus advisor Dr. Anthony Fauci told CNN on Thursday. "We don't want to see a surge under any circumstances, but particularly as we go on the other side of Labor Day and enter into the fall."

Fauci, director of the National Institute of Allergy and Infectious Diseases, added that states such as Montana, the Dakotas, Michigan and Minnesota have recently reported a worrying rise in the percent of tests coming back positive among people ages 19 to 25. 

'Accelerator weekend'

Daily new cases of the coronavirus declined for weeks after they peaked in late July at more than 70,000 per day. But now, daily new cases appear to have plateaued at more than 40,000, according to a CNBC analysis of data compiled by Johns Hopkins University. Average daily new cases are up by at least 5% in 22 states, according to the analysis.  

That level of pervasive spread combined with the holiday weekend have the makings of what Vanderbilt University infectious disease specialist Dr. William Schaffner described as an "accelerator weekend."

"This is another holiday and we will see what the general population does, how careful they are or how carefree they are," Schaffner said. "I have a fair amount of trepidation, frankly, because it looks as though a very substantial portion of our population wants to be out and about very freely in groups, without masks, not paying attention to social distancing."

Schaffner said he has noticed that local officials and individuals have grown increasingly comfortable in recent weeks as cases have declined and much of the public will perhaps let their guard down for the holiday weekend.

'Seesaw effect'

He added that in Tennessee, where he's based, some county officials recently allowed their mask mandates to expire after cases fell to a manageable level. Schaffner said this is a big mistake that might be evidence of a broader phenomenon happening in communities and among individuals across the country, who increasingly feel they can ease their vigilance.

"You will get a seesaw effect and I can predict that just as sure as I know the sun is going to rise in the east ... We've got to sustain this for months. It's not a quick fix," he said. "If there's a tenuous commitment to social distancing and masking and all that, it will blow away over Labor Day."

In addition to Fauci, Adm. Brett Giroir, an assistant secretary for health, has also warned that cases need to continue to fall through Labor Day. 

Not prepared

"We have to go into the fall with decreasing cases like we're doing now," Giroir told reporters on Tuesday. "We can't risk a lack of personal responsibility."

Dr. Syra Madad, senior director of the systemwide special pathogens program at New York City Health + Hospitals, said the country is "nowhere close to where it needs to be" headed into Labor Day. 

"We are not very well prepared as a nation," she said. "Labor Day, obviously, is a milestone, but also you know all of the holidays coming up are big milestones."

Principal Nathan Hay checks the temperatures of students as they return to school on the first day of in-person classes in Orange County at Baldwin Park Elementary School on August 21, 2020 in Orlando, Florida, US. Face masks and temperature checks are required for all students as Florida's death toll from COVID-19 now exceeds 10,000, with some teachers refusing to return to their classrooms due to health concerns.

Madad emphasized that the situation will only become more complex closer to Halloween and Thanksgiving. By then, seasonal influenza will likely have settled in, especially as many schools, which are often sites of flu spread, reopen.

"As we get into some of these other holidays, when the weather changes, it's going to be harder for people to meet outdoors," she said, "so more people will want to congregate inside the homes that, we know, is another high-risk area right there."

new forecast from the Institute for Health Metrics and Evaluation at the University of Washington predicts the U.S. will top more than 410,000 total Covid-19 deaths by the end of the year. The model by IHME, whose models have previously been cited by the White House and state officials, forecasts that the current death toll will more than double by Jan. 1 and could reach as high as 620,000 if states aggressively ease coronavirus restrictions and people disregard public health guidance.

"The worst is yet to come. I don't think perhaps that's a surprise, although I think there's a natural tendency as we're a little bit in the Northern hemisphere summer, to think maybe the epidemic is going away," Dr. Christopher Murray, director of IHME, told reporters on a conference call Friday.

Hurricane season

Madad added that she's concerned about hurricane season. The National Hurricane Center says the season peaks between mid-August and late October. Already this season, Hurricane Laura displaced hundreds of thousands of people in Texas and Louisiana, driving at least a couple thousand into potentially crowded shelters that Madad said could help spread Covid-19.

"You couple that with Covid-19 and it's very, very difficult for people to stay safe when you don't have some of the bare necessities," Madad said.

Hurricanes, as well as other natural disasters such as the wildfires in the West, have also disrupted state health officials' ability to respond to local outbreaks and contain the virus. Louisiana Gov. John Bel Edwards said last week that Hurricane Laura, which has devastated much of southwest Louisiana, has also shuttered many of the state's Covid-19 testing sites.

"The challenge is we're basically going to be blind for this week because we're having to discontinue much of our community-based testing," he said last week. "This comes at a particularly bad time for us because it's two to three weeks since we resumed K-12 education and since we started moving young people back on to college campuses." 

Earlier this week, HHS' Giroir announced that the federal government was surging testing resources to the state in order to help test displaced people and keep them healthy.

Gathering safely

Dr. Ashish Jha, who recently left as director of the Harvard Global Health Institute to become dean of Brown University's school of public health, said there are some ways people can safely meet up this holiday weekend. He said it's possible to safely gather in small groups outdoors but added that people should resist going indoors at all.

"Keep it small. Keep it outside. And you don't have to spend six hours together. Do it a few hours, have a couple of burgers, sit apart, and it's probably reasonably safe," he said. "But have a plan for if it starts raining."

He added that he's "worried" about Labor Day, and epidemiologists across the country will need to "watch the data." Beyond the holiday, he expects the fall "to be a bit of a mess."

"We may have some hard days ahead," he said. "But I remain reasonably optimistic that we're going to get through this. We're not going to have days where 2,000 Americans die from this. I am reasonably hopeful that those days are behind us." Researchers know more about the disease and how to treat it than they did just a few months ago, he noted.

When it comes to a potential vaccine, he said he's more focused on improving treatment and mitigation strategies such as testing, tracing and isolation. Eying the Nov. 3 presidential election, he said he was worried the political calendar will create pressure to authorize a vaccine this fall, before there's enough data to know whether it's truly effective.

"The problem with that is it will tell people they can let their guard down," he said. "That will make behavior and all the other stuff so much harder to manage as we go into November and December, because if people think it's over and we hear a magic bullet is right around the corner, it can make all the public health stuff so much harder."

— Graphics by CNBC's Nate Rattner.