The newly resurgent coronavirus could spark 140,000 to 300,000 cases a day in the United States come August, fueled by the highly transmissible delta variant and the widespread resumption of normal activities, disease trackers predict.

The nation is already reporting more than 70,000 cases a day, according to The Washington Post’s rolling seven-day average – an increase of nearly 60,000 in the daily average in less than six weeks. Cases, measured as that rolling average, have risen to levels not seen in February.

Justin Lessler, a University of North Carolina epidemiology professor who assisted in coordinating pandemic forecasts through the COVID-19 Scenario Modeling Hub, said he was “quite concerned … It worries me that we may have been too optimistic” in projecting lower caseloads into the fall.

The seven-day average of cases nationwide has risen by about 60 percent in the past week alone. Daily hospitalizations rose by roughly 40 percent and deaths rose almost 30 percent, now averaging more than 300 each day.

“It is getting worse, and at least as of right now, it is not really slowing down in the U.S.,” said David W. Dowdy, an associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health.

If there is a silver lining, it is this: Experts do not expect hospitalizations and deaths to rise to the levels they were in the winter. “The people who are getting sick are younger and healthier,” Dowdy said.

The surge has multiple propellants. The delta variant, which transmits more easily between people, is one.

Delta, originally detected in India and first diagnosed in the United States in March, rapidly replaced other variants to become dominant. The Centers for Disease Control and Prevention estimates delta is responsible for more than 8 in 10 new cases.

Another major contributor, epidemiologists said: Relaxing precautions, such as no longer wearing masks or engaging in social distancing. That probably includes behavior even among the vaccinated, Columbia University epidemiologist Jeffrey Shaman said.

Shaman suspects infections among vaccinated people, known as breakthrough infections, are much higher than official tallies indicate. That could be because vaccinated people are less likely to get tested. Or they may be apt to dismiss a mild case of COVID-19, the disease caused by the virus, as simply the sniffles.

“The central issue is that people want to put the pandemic and the virus behind them,” he said, offering as examples unmasked crowds packed into bars and ballparks.

Shaman said his team’s most recent model showed a peak in cases in four to five weeks, at which point there would be “a little over a million cases for the whole week” across the U.S. population, which averages to more than 140,000 cases daily.

Modelers at the University of Washington’s Institute for Health Metrics and Evaluation predict a rise through mid-August, leveling off at about 300,000 cases daily. In that scenario, deaths rise to a September high of 1,500 daily. But if everyone were to wear a mask – an unlikely prospect, institute epidemiologist Ali Mokdad acknowledged – the caseload could be about 10 times smaller.

One measure of the hastening pace of the resurgence: Earlier in July, the COVID-19 Scenario Modeling Hub, a consortium that combines input from multiple academic teams, issued a consensus projection that cases would rise to 60,000 per day in October, based on data through July 4. That case count was passed this week.

No scientific approach can cleanly disentangle the effects of delta from loosened restrictions. That’s because, in the United States, both things happened in the same window of time. Dowdy, of Johns Hopkins, said he would hazard a guess “the effect of changes in behavior over the past three to four months has been much greater than the effect of the delta variant.”

A familiar pattern has emerged in the United States. Relaxed behavior is followed by a spike in cases, which in turn spurs people to take more precautions. Americans are much better at reacting to surges than preempting them, Mokdad said.

Mokdad said the CDC made a mistake when the agency did not push harder for masks a month ago. The CDC on Tuesday issued beefier guidelines for wearing masks, saying that even vaccinated people ought to wear face coverings when in indoor public settings where transmission is high. The agency said it was swayed by data showing vaccinated people can carry as much virus as the unvaccinated do.

This summer surge recently surpassed last summer’s high in terms of case counts. That wave, the country’s second, crested at the end of July 2020 with a seven-day average of below 70,000 daily cases. New infections waned through August and September, and rose again into the winter.

The current wave may soon ease at the “leading edge,” Dowdy said, where it first took off in states such as Missouri. But he believes sufficiently vulnerable populations exist elsewhere for the surge to continue, like a sequence of rolling ocean waves. Cases may crest nationwide within the next three to four weeks, Dowdy estimated.

Over that period, the risk of catching the virus among unvaccinated people is probably similar to what it was in November, he said. And, if this trajectory holds, he predicted a fivefold increase in new infections, which would mean cases would rise to numbers as high as January’s.

These estimates are inexact. Variables such as human behavior and even the weather can influence spread, in addition to viral evolution. Such projections are “very, very hard” to do, Shaman said. “A lot of models have had trouble adjusting to this new variant,” he said.

Forecasts further into the future are more difficult still because they cannot account for new variants.

Models struggle to anticipate sharp dips too, Shaman said. In England, cases are much lower than anticipated after the nation’s economic reopening.

“The U.K. is not necessarily a bad parallel,” said Dowdy, adding that pandemic trends there may resemble the United States 30 days in the future. “If we do nothing in response to this current wave, three or four weeks from now those networks of people – largely unvaccinated and interacting closely – are going to be largely saturated in infection, which is probably what happened in the U.K.”

The public has the power to meet this challenge, the experts said.

Because it takes about five days between getting infected and getting sick, the “things we do right now can reduce the number of infections that happen,” such as wearing masks and avoiding crowds where transmission might happen, Dowdy said.

A torrent of vaccine mandates were recently issued, too, for some federal employees and many other workers, including those at Google and Facebook. There’s already a glimmer that people are responding to this. In California, more people were vaccinated Wednesday than any day in the previous three weeks.

Vaccines work well at protecting people from severe disease and death. But Shaman said he was concerned people are “still capable of passing it on and capable of spreading it,” especially in light of a small study from Israel suggesting the Pfizer-BioNTech vaccine’s ability to protect against infection wanes. Israel recently announced it would give a third Pfizer dose as a booster to adults older than 60.

Data continue to show the vaccines are safe. And the more the virus floods a community, Dowdy said, the greater the benefit of the vaccine’s protection.