Sept. 23 (UPI) -- Becoming ill with both COVID-19 and the seasonal flu is possible, but it's unclear whether one virus makes the other one worse, experts said this week.
With the winter flu season approaching, concerns about co-infection -- being infected with both viruses simultaneously -- with influenza and COVID-19 are valid, they said.
Although documented cases of co-infection are relatively rare, as many as 3% of all COVID-19 patients are also battling another virus at the same time, with influenza being among the most common, researchers estimate.
Whether co-infection worsens the health risk of COVID-19 hasn't been determined, but that could change if the United States faces "parallel pandemics" this winter, Daniel Salmon, director of the Institute for Vaccine Safety at Johns Hopkins Bloomberg School of Public Health, said during a conference call with reporters Tuesday.
"That's the big unknown," added Salmon's colleague, Andrew Pekosz, a virologist and co-director of the Johns Hopkins Center of Excellence for Influenza Research and Surveillance.
"What we do know is that both viruses have similar symptoms, and both can cause serious illness, particularly in certain at-risk populations," he said.
Those "at-risk" groups are the same for both viruses, and include the elderly and people with chronic health conditions like high blood pressure, heart disease and diabetes, Pekosz said.
In a typical flu season, as many as 40 million Americans are sickened with the seasonal virus, but winter of 2020-21 is expected to be anything but typical, officials have said.
Earlier this month, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, warned that COVID-19 cases across the United States were "unacceptably high" heading into flu season and expressed concern that the two viruses could overwhelm the country's healthcare system.
More than 550,000 Americans have been hospitalized by COVID-19, and up to 800,000 require that level of care annually because of the flu, the U.S. Centers for Disease Control and Prevention estimates.
CDC officials recently urged clinicians across the country to consider the seasonal virus, COVID-19 or both when patients experience cough, fever, muscle aches and fatigue.
They also bolstered flu vaccine supplies for the 2020-21 season to encourage more Americans to get the preventive shot.
Although the flu vaccine doesn't protect against COVID-19, getting the shot reduces a person's risk for flu, making it more likely that any respiratory symptoms they develop would be caused by the new coronavirus, Pekosz said.
Because both COVID-19 and the flu are respiratory viruses, and are spread the same way, people can take the same steps to reduce their risk for both, like social distancing, wearing a mask in public and washing their hands regularly, he said.
Researchers also are working on tests that can screen patients for both viruses simultaneously. Diagnostics manufacturer LabCorp announced last week that it has created a test that can identify those with COVID-19, influenza A and B and respiratory syncytial virus, or RSV, another common virus.
The company has applied for emergency use authorization from the U.S. Food and Drug Administration for a testing kit consumers can use at home.
Meanwhile, in an analysis published last week by the Royal Society of Chemistry, researchers said they have developed a test that can differentiate between both viruses with greater than 99% accuracy.
Until the dual tests have been evaluated and approved for wide distribution, separate tests will be needed to accurately diagnose those infected, Pekosz said.
"If you're starting to feel respiratory symptoms and they're starting to seem severe, contact your doctor and have them guide you" as to whether you should get tested and what you should be tested for first, Pekosz said.