The Similarities and Differences Between RSV, COVID, and the Flu Symptoms

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01/19/2023

Respiratory syncytial virus, or RSV, COVID-19 and influenza are different contagious respiratory illnesses that are all driving high rates of infection and high volumes of hospitalizations this winter.

These three viral respiratory illnesses are caused by different viruses, but they do share similar symptoms. As a result, it may be difficult to distinguish what you’ve come down with when you’re feeling under the weather.

RSV, COVID and Flu Symptoms

“These are all essentially viral infections,” says Dr. David Cornfield, the chief of pulmonary medicine and medical director of respiratory therapy at Stanford Medicine Children’s Health in California. “So the commonalities significantly outweigh the differences.”

COVID-19, RSV and the flu spread in similar ways: by virus droplets, such as when an infected individual coughs or sneezes, and another individual breathes those particles in or they land on their eyes, nose or mouth. In some cases, the virus can spread if you touch a contaminated surface and then touch your face before washing your hands.

RSV vs. COVID vs. Flu

“The one that looks the least like the others, in most patients, is RSV,” says Dr. Daniel Culver, chair of the department of pulmonary medicine at Cleveland Clinic's Main Campus in Ohio. “RSV typically is only severe in infants and elderly patients and in people with significant immune deficiency or risk factors for severe disease.”

Other populations with risk factors for a severe disease may include people with underlying medical conditions, such as asthmadiabetes or chronic lung conditions or liver diseases, like cirrhosis.

For most other people who don't fall into those categories, RSV symptoms will be much less intense. They generally will appear more like a common cold.

“RSV presents with significant amounts of mucus from the nose, a cough, itchy and runny eyes, and a relatively low-grade fever,” Cornfield says.

On the other hand, “influenza and COVID are very similar clinically,” Culver says. “They both present with fever, cough, achiness, fatigue. It’s not uncommon to have a headache or sinus congestion or a runny nose.”

“Both of them can have GI symptoms,” he says, like vomiting and diarrhea. With the flu, however, these symptoms are more common in children than in adults, according to the CDC. Also, not all persons with flu will have a fever.

“The famous symptom of a loss of smell, of course, would favor COVID,” Culver adds.

Symptom Onset

How quickly and intensely your symptoms start presenting is another way to tell these three viruses apart.

“Influenza has a pretty rapid onset of action,” Cornfield says.

According to the CDC, flu symptoms typically appear about two days after an individual has been infected. Symptoms can even appear only one day after infection. On the other hand, COVID and RSV symptoms come on gradually. For COVID, symptoms may appear two to 14 days after exposure.

Those infected with RSV typically show symptoms within four to six days after exposure. Symptoms will usually come one-by-one, rather than all at once.

Testing

“The best way to distinguish the three is with testing,” Culver says. “That's the only really reliable way to distinguish (between) the three.”

Culver emphasizes that testing is important for a number of reasons:

  • You can take precautions. “One is that it allows people to understand how long they should take precautions and what kinds of precautions they should take with regards to infecting other folks,” he says.
  • You’ll get the right treatment. “The second reason why is because there are some specific therapies for certain individuals that can be helpful for COVID and for influenza,” he says.

“The best, most common way to test for the vast majority of people is the nasal swab,” Culver says.
COVID, RSV and the flu can all be diagnosed using a nasal swab or throat swab. Your health care provider will swipe a cotton swab on the inside of your nose, or the back of your throat, to collect a sample. The sample is then tested to check for suspected viruses or bacteria.

For COVID, “if you have a home test kit, that's an easy way to start,” Culver says. “If you do a home COVID test kit and it doesn't show what the problem is, and you have any significant risk factor for severe disease, then I would encourage you to contact your health care provider to talk about testing options.”

How Long You’re Contagious

“The most contagious time for all of these is just before symptoms develop and around the first day after symptoms develop,” Culver says. “That's the peak time of infectivity.”

According to the CDC, here’s how long you may remain contagious when you’re infected with RSV, COVID or the flu:

  • RSV. People infected with RSV become contagious a day or two before showing signs of illness and remain contagious for three to eight days. Children and those with weakened immune systems may continue to spread the virus for as long as four weeks after they stop showing symptoms.
  • Influenza. People infected with the flu are contagious at least a day before symptoms develop and up to five to seven days after their illness begins. They’re most contagious in the first three to four days of symptoms, though infants and those with weakened immune systems may be contagious for longer than seven days.
  • COVID. Even if an infected individual doesn’t have COVID symptoms, they can still spread it. Though guidance has been mixed, the CDC recommends isolating for five days and masking for up to 10 days. People who have moderate or severe COVID may remain infectious for longer than 10 days.

“Infectivity for influenza tends to abate pretty quickly as symptoms age. The same thing for RSV,” Culver says.
Whereas with COVID-19, people can still be shedding a significant amount of the virus for up to about a week.

“That’s why quarantining oneself after developing COVID for about a week is an appropriate, socially responsible thing to do,” Culver says.

Precautions for RSV, COVID-19 and Influenza

“Most people would say that an ounce of prevention is worth a pound of cure,” Cornfield says. “The old adage still holds true today.”

With both COVID and influenza, there are effective vaccines available for both pathogens.

“Neither of these things are 100% effective at preventing transmission of the disease,” Culver says. “But what they are quite effective at is decreasing the duration of transmission and decreasing the likelihood of severe disease.”

The bivalent COVID booster is quite effective at both of these things, Culver adds.

This year’s flu vaccine has been providing people with a good amount of immune coverage, too.

“It's not too late to get that vaccination,” Cornfield says.

On the other hand, there’s no vaccine available for RSV yet, but it's not due to lack of effort. Researchers have worked for decades to develop an effective vaccine. In December 2022, Pfizer shared promising data results from Phase 3 clinical trials in older adults, and the company announced that their RSV vaccine candidate was accepted by the Food and Drug Administration for an expedited review process.

Supportive care is really important for RSV.

“Good nasal suctioning seems to be the single most important way to help kids stay out of the hospital.”

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