Accessibility links Skip to main content Keyboard shortcuts for audio player NPR logo Shots THE CORONAVIRUS CRISIS Flu Season Looms And Scientists Wonder How Flu And COVID-19 Might Mix September 3, 20205:21 PM ET Heard on All Things Considered Nell Greenfieldboyce 2010 NELL GREENFIELDBOYCE 3-Minute Listen This negative-stained transmission electron micrograph depicts the ultrastructural details of an influenza virus particle, or virion.Still, "it is quite possible and likely that the two viruses could infect a patient at the same time or, for that matter, sequentially: one month, one virus, and the next month, the other virus," says Michael Matthay, a professor of medicine at the University of California, San Francisco. Both viruses can cause dangerous inflammation in the lungs that can fill the airspaces with fluid, making it difficult to breathe, he notes. Article continues after sponsor message COVID-19 is so new, though, that scientists just don't have enough research to know for sure. Generally speaking, co-infections are common when it comes to respiratory diseases. Helen Chu, an associate professor of medicine at the University of Washington in Seattle, has done studies to screen people with respiratory symptoms for a variety of viruses. From Southern Hemisphere, Hints That U.S. May Be Spared Flu On Top Of COVID-19 GOATS AND SODA From Southern Hemisphere, Hints That U.S. May Be Spared Flu On Top Of COVID-19 One study looked at people who tested positive for SARS-CoV-2 and found that about 20% tested positive for at least one other respiratory virus, such as rhinovirus -- which is a common cold virus -- or respiratory syncytial virus (RSV), which can be serious in infants and older adults. Past research suggests that viruses can have complicated interactions when two are present. An extra virus can do nothing at all, can make an illness more severe or possibly even have some kind of short-term protective effect. For example, it's unclear if rhinovirus can make a bout with flu worse, says Chu. Not everyone agrees on that. Some epidemiological research shows that respiratory viruses can compete with each other in a way that means one virus can suppress the spread of another. RSV and influenza virus are a good example of that, says Meskill, explaining that when both try to infect the same cell, one will win. What's more, when RSV levels in a population tend to be high, levels of flu tend to be low, and vice versa. Tanya Miura, a virologist at the University of Idaho, says that when a new pandemic flu virus swept through in 2009, "it was delayed in certain populations that were having ongoing outbreaks of other respiratory viruses at the time."This Research Project Aims To Fix It HEALTH Trump Administration Plans Crackdown On Hospitals Failing To Report COVID-19 Data Popular on NPR.org NATIONAL Florida's Governor Lifts All COVID-19 Restrictions On Businesses Statewide NATIONAL Federal Judge Ousts Trump's Top Public Lands Chief NATIONAL Missouri Governor And Wife To Host Fall Festival Days After COVID-19 Diagnosis GLOBAL HEALTH Coronavirus FAQs: Why Can't The CDC Make Up Its Mind About Airborne Transmission?BOOKS 'Hench' Counts The Cost Of Those High-Powered Superhero Battles HOME PAGE TOP STORIES VIDEO: Saying Goodbye To RBG Shots READ & LISTEN Home News Arts & Life Music Podcasts Programs CONNECT Newsletters Facebook Twitter Instagram Contact Help ABOUT NPR Overview Finances People Press Public Editor Corrections GET INVOLVED Support Public Radio Sponsor NPR NPR Careers NPR Shop NPR Events Visit NPR terms of use privacy your privacy choices text only (C) 2020 nprANALYSIS Partisan Reaction To Loss Of Ginsburg Shows How Much Else Has Been Lost NPR Editors' Picks ELECTIONS Biden Responds To Trump Court Pick: 'Health Care Is On The Ballot' NATIONAL In California, Windy, Dry Weather Expected To Bring 'Critical' Fire Conditions ELECTIONS Michigan Secretary of State Says At Least 3 Million Expected To Vote By Mail WORLD What Does It Take For A Palestinian American Baby To Travel From Israel To The U.S.?wonders Stacey Schultz-Cherry, an infectious diseases researcher at St. Jude Children's Research Hospital in Memphis, Tenn.More Stories From NPR HEALTH In The Era Of Hygiene, 'Clean' Author Makes The Case For Showering Less POLITICS What To Know About Those $200 Drug Cards President Trump Promised HEALTH Coronavirus Maps: How Severe Is Your State's Outbreak?The flu isn't completely absent, though.