Although COVID-19 has some symptoms in common with seasonal influenza, it can be more severe than the flu—and deadlier. Between 24,000 and 60,000 people in the United States died from the flu last season, according to figures from the US Centers for Disease Control and Prevention (CDC). Worldwide, an average of 390,000 people die of the flu each year. The coronavirus, on the other hand, has killed more than 130,000 people in the United States and more than 500,000 worldwide just through June this year, according to a coronavirus tracker established by Johns Hopkins University.

Knowing the symptoms of both COVID-19 and the flu, as well as their similarities and differences, is critical to preventing spread of the infection and seeking medical care if symptoms worsen with either condition.

Symptoms

Fever, fatigue, cough, sore throat, and achiness are common for both COVID-19 and the flu.

Chills, dry cough, shortness of breath, a sudden loss of smell and taste, nausea or vomiting, and diarrhea are more prevalent in COVID-19.

Approximately 20 percent of patients with COVID-19 have moderate to severe symptoms. Of those patients, less than half a percent are hospitalized. The most common symptom in moderate cases is difficulty breathing. In more severe cases, patients have experienced strokes and heart attacks, and many have died—outcomes that may be linked to the virus' impact on blood vessels.

In some cases, neurologic symptoms have been reported, including loss of taste and smell, delirium, dizziness, confusion, numbness in hands and feet, seizures, muscle weakness, and Guillain-Barre syndrome.

Transmission

The flu and the coronavirus are thought to spread primarily in droplets released from the nose and mouth of an infected person. This can happen through talking, laughing, singing, sneezing, or coughing when people are in close proximity. The risk of transmission decreases if you stay at least six feet apart from others, interact outdoors, and wear masks.

While less likely, you also can catch either virus by touching a surface an infected person has touched and then putting your hand to your mouth or nose, which can transfer germs to the respiratory tract.

With COVID-19, many people seem to be contagious before they have symptoms; with the flu, people become contagious three to four days after symptoms begin. Wearing a mask can help protect you and others.

Treatment

Rest, fluids, and medication to reduce fever (such as acetaminophen) are standard treatments for both flu and COVID-19 in cases that don't require hospitalization. If you have mild symptoms of COVID-19, you should take your temperature before taking each dose of fever reducer. Call your doctor if your temperature goes above 100.4 degrees or if any other symptoms worsen.

No vaccine currently exists for COVID-19. For the flu, a new vaccine is developed each year that matches that year's dominant strains of the virus. While a vaccine doesn't prevent the flu 100 percent of the time, it can prevent cases and reduce the illness' severity.

Flu Season

Getting a flu shot is especially important this year for several reasons. First, the flu kills thousands of people each year. Second, you risk contracting COVID-19 in the hospital if you are admitted for severe flu symptoms. Finally, contracting the flu and COVID-19 simultaneously may result in more severe illness and may lower your defenses in combatting the coronavirus.

Ask your doctor's office to alert you when flu shots are available and inform you of the precautions the office is taking. If you opt for a flu shot at a supermarket, pharmacy, or urgent care clinic, call to find out if an appointment is required. Wear a mask and respect social distancing rules, such as where to wait for your turn.

Dr. Sejvar is a neurologist and epidemiologist at the US Centers for Disease Control and Prevention.