There are many aspects of the virus that remain unknown for scientists but older viruses offer some clues.
People usually get infected by four common coronaviruses that were first identified in the mid-1960s, according to the US Centers for Disease Control and Prevention. And those tend to peak in the winter months.
Dr. Greg Poland, a professor of medicine and infectious diseases at the Mayo Clinic, said that SARS-CoV-2, the technical name for the novel coronavirus that causes Covid-19, is likely to follow that pattern.
If that happens, a second wave of the virus would return just in time for the start of flu season. The flu has been a constant threat for Americans and devastating in recent years. The CDC estimates there were at least 39 million cases of the flu in the US and at least 24,000 deaths during the 2019-2020 season.
Poland, the director of the Mayo Clinic's Vaccine Research Group, says the combination of a second wave of Covid-19 with flu season could create "a lot of confusion" because of their overlap in symptoms and put a heavy strain on the health care system.
It wouldn't be the first pandemic to come back in force. In 2009, the US experienced a wave of cases of the H1N1 influenza virus, known as swine flu, in the spring. Months later, a second wave was reported in the fall and winter, the CDC says.
The 1918 influenza pandemic, which killed 50 million people globally and about 675,000 Americans, appeared as an initial mild spring wave in the US before a lethal second wave hit the country in September.
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