7 Signs You May Have Had COVID-19 Without Realizing It, According to Doctors

Whether you had a “bad cold” this winter or recently endured a cough that would not quit, it’s only natural to wonder if you might have had COVID-19 without realizing it. That’s especially true now that infectious disease experts say the virus was likely already spreading before cities started to lock down and put social distancing orders in place.

“As the weeks progress, it’s become evident that this is a virus that was widespread throughout our country, particularly in more populated areas, sooner than we thought,” says William Schaffner, M.D., an infectious disease specialist and professor at the Vanderbilt University School of Medicine.

So, could you have had COVID-19 without realizing it? It’s possible. “Most people who have coronavirus have an uncomplicated case of infection, and it could be indistinguishable from the cold or influenza,” explains infectious disease expert Amesh A. Adalja, M.D., senior scholar at the Johns Hopkins Center for Health Security. Plus, some people have no symptoms at all—up to 40% of infections, according to estimates from the Centers for Disease Control and Prevention (CDC).

Unfortunately, there’s no way to know with 100% certainty if that illness you dealt with last winter was COVID-19 or if you happened to pick up an asymptomatic case at some time. But experts say some signs can be tip-offs that you might have had COVID-19 already. Here are the top ones to know, plus what it means for immunity.

1. You had a “bad cold.”

Early in the pandemic, people believed that COVID-19 didn’t start circulating in the U.S. until late February and March. New research from the University of Texas suggests otherwise. For the study, scientists analyzed throat swabs taken last winter in people who had suspected flu cases. These swabs were done in Wuhan, China (where the novel coronavirus originated) and Seattle, Washington (where the first case of COVID-19 was confirmed in the U.S.).

The researchers discovered that for every two cases of the flu, there was one case of COVID-19. As a result, they believe COVID-19 likely arrived in the U.S. sometime around Christmas.

“It took longer to get out to rural areas so, if you were on a farm this winter and you had the sniffles, you probably just had a cold. If you were in New York City or another major city, you might have had a COVID infection and never knew it,” Dr. Schaffner says.

It can be tough to distinguish a cold from a mild form of COVID-19 without a test, depending on which symptoms you experience, he says, but colds don’t typically cause shortness of breath, severe headaches, or gastrointestinal symptoms like COVID-19 can. Here’s the full list of the CDC’s official symptoms:

• Fever or chills
• Cough
• Shortness of breath or difficulty breathing
• Fatigue
• Muscle or body aches
• Headache
• New loss of taste or smell
• Sore throat
• Congestion or runny nose
• Nausea or vomiting
• Diarrhea

2. You lost your sense of smell or taste at one point.

Loss of smell and taste has been a big hallmark of COVID-19. While this symptom doesn’t occur for everyone, Dr. Adalja points out that it’s now strongly linked with the novel coronavirus.

Preliminary data from the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) found that, in COVID-19 patients who lost their sense of smell, 27% had “some improvement” within about seven days, while most were better within 10 days.

Worth noting: It’s also possible to temporarily lose these senses with other respiratory conditions, like a cold, the flu, a sinus infection, or even with seasonal allergies. But experts say that the symptom can linger in some people and last for months after recovering from COVID-19.

3. You’ve been dealing with unexplained hair loss.

This hasn’t been widely studied in the context of COVID-19, but many people who have recovered from the virus are reporting issues with hair loss. Actress Alyssa Milano, who has been suffering from COVID-19 symptoms for months, shared a video of herself on Instagram in early August repeatedly brushing out large clumps of hair after she showered.

Members of Survivor Corps, the Facebook support group for people who have had COVID-19, have also talked about experiencing hair loss months after recovering from the virus. It’s due to a condition known as telogen effluvium, and it can be caused by a slew of factors, including pregnancy, extreme stress, weight loss, and illnesses other than COVID-19, Dr. Adalja says.

It’s unlikely that you would just lose more hair than usual without having other COVID-19 symptoms, like a cough or fever, Dr. Adalja says. It’s also important to note that hair loss can happen from stress in general, he says—and there’s been a lot of stress due to the pandemic. If you’re experiencing hair loss, it’s possible it’s due to an unknown COVID infection, a build-up of stress during uncertain times, or another underlying issue.

4. You feel breathless sometimes.

Research published in the journal JAMA has found that people with COVID-19 can have after-effects of the virus, including shortness of breath. It’s not entirely clear why at this point or how long this can last, but it’s likely due to lasting inflammation in the lungs.

“This is one of the well-known lingering effects in people who were diagnosed with COVID-19,” Dr. Schaffner says. “If you have this, well, perhaps that illness you experienced before was actually COVID.” If you’re experiencing shortness of breath, call your primary care physician for guidance or ask for a referral to a pulmonologist. They can often prescribe medications and treatments, like an inhaler, that can help, Dr. Schaffner says.

5. You have a cough that will not go away.

A lingering cough is another symptom that people who participated in the JAMA study reported. The cough is often dry, meaning that nothing comes up, like like phlegm or mucus, Dr. Adalja says. This is fairly common: Data from the CDC found that 43% of people who had COVID-19 still had a cough 14 to 21 days after getting a positive test for the virus.

6. You’re really, really tired.

This is one of the biggest lingering effects after a person has COVID-19, according to the JAMA study. That study found that 53% of patients said they were struggling with fatigue around 60 days after they first showed signs of the virus.

“We’re seeing some people who had mild illness who have fatigue for some period of time,” Dr. Adalja says. But, he says, it’s not entirely clear right now why this happens. It could be the way a person’s immune system reacts to the virus, or it could simply be the way the virus works in the body.

Keep in mind that fatigue is a really common issue and can be a sign of many different health issues (including, of course, not getting enough sleep). Like hair loss, people who experience fatigue due to COVID-19 would have also had other symptoms of the virus in the past, Dr. Adalja says.

7. You have unusual symptoms that seem to be lasting forever.

Experts stress that COVID-19 is still a new virus, so doctors and scientists are learning more about it all the time. Research on lasting effects of the virus is ongoing, and it’s difficult for doctors to say at this time that having certain symptoms could mean you had a COVID-19 infection, while others don’t, Dr. Adalja says.

It’s worth mentioning that some people have experienced heart issues after contracting the virus. One small study of 100 people who recovered from COVID-19 that was published in JAMA Cardiology did MRIs on former patients and found that 78% had some kind of abnormal heart finding, independent of any pre-existing conditions. This also didn’t seem to be linked to severity of illness, the researchers found. That could show up in a lot of different ways, including random heart palpitations, Dr. Schaffner says, but it could also be unnoticeable.

Of course, there are plenty of other complications that experts may not even know about yet. If you’ve been feeling off and your symptoms are persistent, Dr. Schaffner says it’s a good idea to get checked out by your doctor, whether you think it’s related to COVID-19 or not.

What about an antibody test?

While an antibody test may tell you if you have had COVID-19, they’re not exactly known for their accuracy. “Antibody tests are getting better, but there are a lot of antibody tests out there that are still unreliable,” Dr. Schaffner says. The Food and Drug Administration (FDA) issued an emergency use authorization for these tests in the spring, but later removed certain tests due to “significant clinical performance problems.”

The CDC also stresses that antibody tests “are not 100% accurate and some false positive results or false negative results may occur.” So it’s possible to test positive for COVID-19 antibodies, but not actually have them.

This comes down to various factors. First, there are other coronaviruses known to cause the common cold, and those can get picked up by your antibody test, skewing the results. What’s more, if you’re only in the first days of the infection, antibodies may not be detected at all because your immune system has not built up a response yet. (Learn more about COVID-19 antibodies here.)

Does possibly having COVID-19 in the past mean you won’t get infected again?

While the above signs could be an indication that you had COVID-19, they can also be caused by other illnesses. “Certainly a lingering cough and fatigue are well known to be a consequence of influenza—just because you have those doesn’t mean you had COVID-19,” Dr. Schaffner says.

Ultimately, short of having a positive test for COVID-19 when you’re ill, it’s hard to know with total certainty if you’ve had the virus. Still, “there are definitely people who got infected and didn’t notice,” Dr. Adalja says.

With all that in mind, there is one important thing to remember: Even if you did have COVID-19 in the past, that doesn’t necessarily mean you won’t get infected again. The CDC specifically states that it’s unclear at this time if people can be re-infected with the virus—and the first case of reinfection was just confirmed in Hong Kong.

So, even if you suspect you contracted COVID-19 before the pandemic really hit, it’s important to continue practicing prevention methods like wearing a mask, washing your hands regularly, and practicing social distancing when you can, both to protect yourself and others.

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