Is it a Cold, the Flu, COVID? How to Tell the Difference.

Let's start with the flu and COVID. Both are contagious respiratory illness and affect the lungs. Both spread in similar ways. However, they are caused by different viruses. Human influenza A and B viruses cause seasonal epidemics of disease (known as the flu season) almost every winter in the United States. COVID-19 is caused by a new coronavirus (called SARS-CoV-2),

Many of us feel confused as scientific research hurries to keep pace with the spread of the novel virus itself. Information about the disease, and guidance for self and community protection seem to change from one day to another, one place to another.

What We've Learned So Far

Since the pandemic was declared back in March, we’ve learned from ongoing scientific research:

• Even though elderly people, especially those with serious underlying health conditions, are most at risk of contracting COVID, people of any age, including infants, can become infected, experience severe illness, and even die.
• The virus can produce a wide diversity of symptoms. It can infect and damage most, perhaps all, organ systems. While it’s generally considered a respiratory disease, infected people may have no cough or runny nose.
• People usually begin experiencing symptoms within 14 days after exposure to an infected person.
• People of any age may “have” COVID with very mild symptoms, or no symptoms at all, but still infect others even though they don’t feel sick themselves. 
• Researchers have determined that people may be contagious 48 to 72 hours before they feel symptoms, and are more likely to spread the illness then, because they aren’t taking steps to protect others: masking, maintaining a physical distance, avoiding crowds.
• What at first may seem like a mild case with only minor symptoms may turn into severe disease within a few days or even weeks later.
• When infected people exhale, talk, laugh, or sing, the virus becomes airborne. It can produce aerosols (fine particles that hang around suspended in the air) that remain infective for many hours. The danger increases when people gather together in enclosed spaces, talking, singing, or laughing.
• People who get COVID may suffer a wide array of long-term effects that appear or persist long after they’ve tested negative: exhaustion, racing heart, blood clots, headaches, vision changes, loss of taste and smell or hearing, impaired mobility, numbness in extremities, tremors, memory loss, cognitive impairment, and mood changes. These “long-COVID” effects (victims are nicknamed “long haulers”) may be worse than the active infection was, and physicians can't yet predict who will experience them or how long they will last. 
• Psychological aftereffects are common. A recent study found that one in five COVID patients developed signs of mental illness within 90 days.

Symptom Checker (COVID, Cold, Flu)

(Note: Learning continues to evolve.)

COVID Versus Flu Symptoms

Many COVID symptoms overlap or coincide with symptoms of other infections/conditions, some of them especially common during the dark winter months, such as colds, flu, sinusitis, various pneumonias, worsening asthma and allergies. Less frequently, COVID symptoms may also overlap or coincide with strep throat, Lyme disease (and other tick-borne infections), mononucleosis, and norovirus (“stomach flu”) infections. 

Here’s a list of the currently known COVID symptoms and their possible overlap with other illnesses/conditions. Keep in mind the learning is growing and this will change over time.

No to Little Overlap

• New loss of smell and taste: This is among the most common early indicators of COVID infection; it's often sudden may persist long after the virus is no longer present.  Flu does not instantly affect a person's taste or smell. 
• Trouble breathing that gets worse with exertion: This is not a common flu symptom. However, it is a common indicator of COVID if it later appears in combination with other symptoms such as cough and/or fever; it rarely occurs in the first days of a COVID infection. If no other symptoms are present, the breathing difficulty likely has another cause.
• Stuffiness/runny nose: This is more often a common symptom of colds, seasonal allergies. It can sometimes occur in flu and is not common with COVID. 
• Neurological symptoms sometimes occur with COVID, but not flu. These include tingling or numbness in the hands and feet, dizziness, confusion, delirium, seizures, and stroke.

Another difference: If a person has COVID-19, it usually takes longer to develop symptoms than if they had flu. Typically, a person develops flu symptoms anywhere from 1 to 4 days after infection. With COVID-19, a person often develops symptoms 5 to 7 days after being infected but also as late as 14 days. 

Overlap

• Headache: This is a very common symptom of flu. It is sometimes a symptom of COVID.
• Cough: This is one of the most common symptoms any respiratory illnesses, so it's common in both COVID-19 and the flu. It's also common among smokers and may occur as a side effect of some blood-pressure drugs. The COVID-19 cough is usually dry, and may become severe. 
• Whole-body achiness, exhaustion: This is a common symptom of flu and sometimes occurs with COVID-19. 
• Sore throat: This is sometimes a symptom of COVID as well as flu. A sore throat could also be a symptom of a bacterial strep infection, especially if you also have swollen glands.
• Fever/chills: This is common for both flu and COVID and infectious diseases, but not everyone with COVID will have a fever.

If you believe you have COVID symptoms...

If you've been exposed, if you feel sick, or if someone in your household feels sick, then self-quarantine indoors. You must quarantine, even if you feel good the whole time. What is quarantining? This means staying home, separating yourself from others, monitoring your health, and following directions from their state or local health department. As of now, the time from start to end of quarantine is 14 days but this may change in the future as we gain more learning. Critically important—a negative Covid test doesn't mean you don’t have Covid—so continue to quarantine for the entire recommended time. 

If you or anyone in your household does experience COVID symptoms, call your doctor to see if s/he recommends getting tested. Even before a diagnosis, isolate the sick person in one room if possible away from others, and quarantine other household members. Everyone should wear masks indoors, wash their hands frequently, and wear disposable gloves when handling items the sick person has touched. Disinfect all common surfaces, eating and cooking utensils.

Monitor mild symptoms at home, but if they get worse, call your doctor for advice. Seek immediate medical attention for symptoms that progress rapidly, especially chest pain, difficulty breathing, confusion, spike in fever, or blue lips.

Despite what they’ve already discovered, researchers say there’s still a lot we don’t know, so expect the information firehose to keep pumping. Stay tuned.

Learn more

• COVID-19 basics Take a gander at this excellent explainer from Harvard Health to help you understand the dizzying information blizzard around the virus, and why it may keep up for some time.
• Swiss cheese model of viral protection: Stack the layers of personal and shared responsibilities to plug the holes that allow respiratory viruses to infect us.
• Please! Learn to wear a mask properly  
• Consider adding a face shield, not as a substitute for a mask, but in addition to a mask as an additional layer of protection. 

Reviewed and edited for medical accuracy by infectious disease expert and physician Dr. Judy Stone