What Happens if You Get Both COVID and Flu (or RSV) at Once?

5 min read

Nov. 8, 2023 – Getting COVID-19: No fun. The same is true of flu or RSV. But getting more than one of them at the same time? Now you’re talking about what could be a really dangerous situation. 

As the colder months creep up on us, so does the spread of the big three respiratory viruses: COVID, influenza, and respiratory syncytial virus. The good news is we now have an updated COVID vaccine, flu shots that protect against multiple strains of the virus, and RSV vaccines for older folks, pregnant people, and infants. Yet despite our prevention efforts, some unlucky few may contract not just one of these viruses, but two at once or in close succession during the winter season. 

While we can’t predict what the season will look like this year, last year’s data from the CDC showed that RSV, COVID, and flu didn’t all peak at once – which is good news for both patients and health care systems. 

Here’s why that’s good news: Last winter was the first time Panagis Galiatsatos, MD, a pulmonary and critical care doctor at Johns Hopkins, saw patients coming in with both COVID and flu. Far more often than not, he said, patients had only one of these viruses; still, the number of those with both flu and COVID he saw last year was “alarming.” 

“Patients that had co-infections were by far our sickest patients,” Galiatsatos said. “This is also a clinical bias because I’m a critical care physician, but all of the patients I met with co-infections were in the intensive care unit.”

How Do You Know If You Have More Than One Virus? 

When it comes to just how many people experience co-infections like this, it’s hard to tell. Most of these diagnoses come from being hospitalized, where doctors will typically test for all three viruses. For those who don’t end up in a hospital, they might not know they have more than one infection, especially because the symptoms are similar. A runny nose, cough, fever, and body aches can happen with all three viruses. 

Because of the accessibility of COVID tests, it’s more likely that if you get sick and test positive for COVID, you probably won’t seek out a flu or RSV test at a medical facility if your infection isn’t dire enough to prompt a hospital visit. 

Testing for all three isn’t a necessity for everyone, said Peter Chin-Hong, MD, an infectious disease expert at the University of California, San Francisco. The elderly, very young, and people with weakened immune systems should definitely seek further testing as soon as they’re able to. 

However, those who don’t fall into those categories can still get tested for all three viruses. Based on what doctors have seen in the past, there’s a higher chance that if you have two viruses, it’s probably COVID and flu, not RSV. And early testing in these cases can save patients a lot of grief because we have antiviral treatments for flu and COVID that we don’t have for RSV. 

What to Do If You Have Flu and COVID 

“First thing is, don’t panic,” says Chin-Hong. If you test positive for COVID at home and you have symptoms, seek out the drug Paxlovid within 5 days of being sick. If it turns out you have the flu as well as COVID, you can get antivirals like Tamiflu within the first 48 hours of symptoms, which may shorten the illness by a day or more. 

There’s been some confusion around who exactly qualifies for Paxlovid. The FDA has said that it is approved for the treatment of “mild to moderate COVID-19 in adults who are at high risk of progressing to severe COVID-19,” but some may assume they aren’t in the high-risk category and don’t seek it out. 

There is still a reluctance to take Paxlovid, from patients who are worried about the “rebound” and from doctors who are hesitant to prescribe it, said Bernard Camins, MD, an infectious disease expert at Mount Sinai in New York City. 

“We need to be more willing to prescribe Paxlovid as physicians,” Camins said. “Sometimes doctors will say, ‘Oh, you’re not feeling too bad, let’s not do it.’ The problem is it might be too late by the time [the patient] does get sick enough.” 

Regarding the infamous COVID rebound -- where patients develop COVID again shortly after recovering -- that many have associated with Paxlovid use, doctors like Chin-Hong and Camins want patients to know that this rebound is pretty typical, with or without Paxlovid. 

And in the respiratory virus season in particular, Chin-Hong said, what you might think is a rebound of COVID symptoms may very well be another virus, like influenza or RSV. 

Does One Virus Make You More Susceptible to Getting Another? 

The short answer: It depends on who you are, what activities you do, and the timing of your infection. 

Studies on COVID have shown that there can be long-term damage to immune systems after recovering from an infection. Sometimes having two viruses at once can make you sicker, as was the case for Galiatsatos's patients. Researchers have also found that patients who tested positive for influenza had a decreased risk of testing positive for COVID; but for those who did have co-infections, the disease was much more severe and left even more long-term damage to the lungs. 

Having COVID is the most common denominator when it comes to people with multiple infections, Galiatsatos said, due to its ability to invade the immune cells, weakening patients and making them more vulnerable to catching other viruses. 

But there is still a lot we don’t know about co-infections with COVID, flu, and RSV. According to William Schaffner, MD, an expert in preventative medicine and infectious diseases at Vanderbilt University in Nashville, a non-immunocompromised person isn’t more likely to get infected with another virus if they already have one. 

“That is, unless their behaviors lead them to greater exposure,” Schaffner said. “If people aren’t vaccinated, don’t wear masks, or have a personal behavioral disposition to constantly expose themselves to vociferous crowds, well, they're more likely to pick up one or more of these infections during the course of the winter. 

“That’s simply because they're exposing themselves. It doesn't have anything to do with their immune systems.”