Which is it: the flu, RSV, or COVID?

Flu, COVID, RSV — Photo by Leeloo, Prexel

Parents ask us every day the difference between the flu (influenza), RSV (respiratory syncytial virus), or COVID (coronavirus disease 2019). While no method is fool proof, here are some typical differences among these viruses:

The flu, caused by influenza virus, comes on suddenly and makes you feel as if you’ve been hit by a truck.

Flu almost always causes fever of 101°F or higher and some respiratory symptoms such as runny nose, cough, or sore throat (many times, all three). In addition to the usual respiratory symptoms, the flu causes

body aches, headaches, and often the sensation of your eyes burning. Fever can last 5-7 days. Children, more often than adults, can vomit and have diarrhea along with their respiratory symptoms, but contrary to popular belief, there is no such thing as “stomach flu.” All symptoms come on at once; there is nothing gradual about coming down with the flu.

COVID can cause the same symptoms. Since home COVID tests are readily available, you can answer the question of “Flu or COVID?” at home.

Colds, even really yucky ones from RSV, come on more gradually.

RSV, a common cause of the common cold, is notorious for causing very thick mucus. The mucous is why some babies and young children have more severe coughing and breathing difficulties with this particular cold virus. Our immune systems are not good at mounting a lasting immunity to RSV so kids and adults tend to get this virus again and again. The first time someone is hit with RSV is usually their worst episode.

Symptoms usually start out with a sore throat or mild runny nose. Gradually, the nose runs more and a cough starts. Sometimes RSV can cause fevers for a couple of days and some hoarseness. Children are often tired from interrupted sleep because of cough or nasal congestion. This tiredness leads to extra crankiness. To further complicate things, Covid can cause identical symptoms.

Usually kids still feel well enough to play and attend school with colds like RSV.

The average length of a cold is 7-10 days although sometimes it takes two weeks or more for all coughing and nasal congestion to resolve.

Wondering about the color of mucus?

The mucus from a cold can be thick, thin, clear, yellow, green, or white, and can change from one to the other, all in the same cold. The color of mucus in the first few days does NOT tell you if your child needs an antibiotic and will not help you differentiate between a cold and the flu.

So, is it the flu, RSV, or COVID?

Flu = sudden and miserable
Colds, including RSV = gradual and annoying
COVID = either

If your child has several days of runny nose and cough, but is drinking well, playing well, sleeping well and does not have a fever, the illness is unlikely to “turn into the flu.” A home test can help tease out COVID from a cold or the flu.

And yes, a kid can have multiple respiratory viruses at the same time. Let’s hope that does not happen this winter.

Julie Kardos, MD and Naline Lai, MD