Confirmed coronavirus cases across the U.S. topped the 8 million mark Friday as the pandemic begins to overlap with flu season, according to data compiled by Johns Hopkins University.

More than 218,000 people are currently known to have died of the virus.

Public health experts have long worried about about the U.S. health care systems ability to handle coronavirus and influenza cases at the same time. If hospitals become overwhelmed, it will be difficult for people to get the care they need.

Robert Redfield, director of the Centers for Disease Control and Prevention , painted a bleak picture in July of the coming fall and winter months, saying it is probably going to be one of the most difficult times that we have experienced in American public health.

I am worried, he said in an interview with the Journal of the American Medical Association.

Warmer weather allowed people in regions severely affected early in the pandemic to gather more safely outdoors, helping to keep COVID-19 cases down in the former hot spots of New York and New Jersey. But across much of the rest of the country, the coronavirus began spreading rapidly during the late spring and summer months as lockdown measures lifted in areas where hospital resources were not initially strained.

Some states, such as Texas and Arizona, managed to curb new cases by late summer but are now facing a potential resurgence.

Others, such as North Carolina and Illinois, are seeing an alarming rise in new cases.

With the impending flu season and colder weather forcing people back indoors not to mention the upcoming holiday season worries are growing about an autumn spike. Researchers believe the coronavirus spreads much easier in enclosed spaces where air containing the virus can recirculate in the absence of good ventilation. Viruses also generally travel better in dry winter air.

Dr. Anthony Fauci the nations leading expert on infectious disease who has been sidelined by President Donald Trump warned in early August that the U.S. needed to get new coronavirus cases down to fewer than 10,000 per day by September.

If we dont get them down, then were going to have a really bad situation in the fall, Fauci said in an interview with the Journal of the American Medical Association.

That has yet to happen. On Thursday, the number of new daily cases topped 60,000 for the first time since early August.

Wisconsin also opened the doors to a field hospital this week outside Milwaukee that can handle more than 500 patients. The states deputy secretary of health services, Julie Willems Van Dijk, said Wisconsins overall health system is in crisis. Many intensive care units are strained, and hospitals all over the state report current and imminent staff shortages, she said.

A coronavirus vaccine is still in the works. U.S. drugmaker Pfizer one of the leading contenders developing a vaccine said it may know whether its design is effective by the end of October. But the company does not plan to apply for an Emergency Use Authorization from the government, which would allow it to distribute the drug, until the second half of November.

Regardless of the exact timing, experts said it may take several months to vaccinate a significant portion of the population.

In the meantime, states and municipalities will need to rely on testing ability, which has generally improved since the spring. Different methods of testing that are currently being adopted, such as pooled tests, may also improve the speed of results.