MINNEAPOLIS >> The growing COVID-19 pandemic could last up to two years, with a potential second wave in the fall, according to nationally renowned University of Minnesota epidemiologist Michael Osterholm and a team of researchers.

The exact path the disease will take is unclear, but with no vaccine and a global population that had no immunity to the new coronavirus, COVID-19 could follow patterns seen in previous pandemics.

That means that governments will need to continually adjust their pandemic responses to waves of infections, which could have several peaks, rather than a distinct period of illnesses that burns out in a matter of months.

“We are learning how to die with this virus and we have to learn how to live with it,” said Osterholm, director of the Center for Infectious Disease Research and Policy at the U and a frequent infections disease expert on national cable news programs.

Dr. Anthony Fauci, the nation’s top infectious disease physician, said this week that he thinks a fall wave of new cases was “inevitable.”

Reviewing eight global influenza pandemics over hundreds of years, the researchers noted that three pandemics since 1918 have been characterized by an initial wave of cases in the spring, followed by a larger wave in the fall.

The first wave tend to be concentrated in some areas, subsides during the summer and then becomes widespread in the fall.

“In the first wave of a flu pandemic you have a hit-and-miss phenomena, some cities are hit hard and some are not,” Osterholm said. “When the big wave came around in the fall that is not the case.”

It is still unclear what leads to the wave patterns, Osterholm said, but the virus will continue its spread until a critical mass of the population develops immunity through infection — roughly 70%. Right now, an estimated 5% to 6% of people have been infected, and even then it is unclear how long immunity will last.

COVID-19 caught people off guard even as it was emerging in China in mid-December.

“Even the most experienced international public health experts did not anticipate that it would rapidly spread to create the worst global public health crisis in over 100 years,” the researchers noted.

In the United States, most public health surveillance systems at the beginning of the year mistook COVID-19 for the flu, which has similar symptoms, according to a study released today by the Centers for Disease Control and Prevention in Atlanta. Additionally, there was a widespread shortage of tests that could detect the new coronavirus.

Cases were also being imported from travelers returning from China as well as Europe, and cruise ship passengers played a role as well.

Those included 101 people, including a few Minnesotans, who cruised the Nile River in February or early March and later tested positive, the CDC noted.

Their return to 18 states doubled the number of known cases in the country at the time.

Even if there had been earlier testing in the United States, COVID-19 would have ballooned to become a major public health problem.

“Even those who did early testing, they are constantly fighting this,” Osterholm said. “Singapore is in a state of emergency. Japan is in a state of emergency.”

Still, the nation should develop a comprehensive strategy to provide more testing, including marshaling the chemicals, cotton swabs and personal protective gear needed to conduct testing.

“To say I am frustrated would be a gross understatement,” Osterholm said.

Minnesota has seen significant gains in its testing numbers, with about 4,500 tests performed Thursday. As a result, the number of positive cases continues to climb, with 594 new infections announced today.

Twenty-eight deaths were also announced, bringing the state’s total to 371 fatalities. About 80% of the deaths have been among residents of long-term care facilities.

There are 221 nursing homes or assisted-living facilities that have at least one case in a resident or staff member, with 21 facilities that have 20 or more cases. But about half of the facilities have one or two cases, noted Kris Ehresmann, infectious disease director at the Minnesota Department of Health.

She added that asymptomatic transmission of the virus means that some staff members who got infected in their communities may have unwittingly brought COVID-19 into the facilities.

The diagnostic test usually cannot detect the virus in someone who doesn’t have symptoms.

Still, the state’s plan is to test more people who do have symptoms so those who are infected can be isolated, stopping the chain of spread.