First, you may have a slight sniffle. Then, you’re fatigued and feverish. As we navigate the latest medley of winter viruses and you start feeling unwell, you may wonder: “Is it flu or COVID?”

“Both flu and COVID are respiratory illnesses caused by viruses, and they share some similar symptoms,” said Kathleen Cameron, former Senior Director of the NCOA Center for Healthy Aging. “But there are important differences in how the viruses behave, spread, and affect older adults.”

Understanding the distinctions between flu and COVID can help you make smart choices and take steps to protect yourself and others. 

How do I tell if I have COVID vs. the flu?

The flu and COVID vary in several key areas: cause and transmission, symptoms, infectious phase, treatment, and complications. We break down the differences below.

Cause and transmission

• Flu: The flu is caused by influenza viruses, with two main types that trigger seasonal outbreaks—influenza A and influenza B.
• COVID: This illness is caused by the SARS-CoV-2 virus, a novel coronavirus that emerged in 2019. Since then, several strains of the virus have taken hold in the U.S., each with unique subvariants. The dominant variants circulating nationwide as of June 2025 include NB.1.8.1, LP.8.1, and XFG.

Flu and COVID are spread in similar ways, mainly through respiratory droplets when an infected person coughs, sneezes, talks, or breathes. These droplets can be inhaled by people nearby, typically within a range of about six feet.

Additionally, smaller particles (aerosols) from both viruses can linger in the air, especially in enclosed spaces with poor ventilation—and this can spread the viruses over longer distances. However, it’s believed that COVID spreads more easily than the flu.

These viruses may also spread when a person touches surfaces or objects recently contaminated with the virus (like doorknobs), and then touches their face—especially the mouth, nose, or eyes.

Symptoms

Both the flu and COVID are caused by viruses that mainly affect the respiratory system. Their symptoms overlap to a great extent, and it’s not always easy to tell them apart. The chart below highlights the most common flu and COVID symptoms versus the common cold.

Flu vs. COVID vs. the Common Cold

How fast do you get symptoms after becoming infected? If you have the flu, you'll likely start experiencing symptoms within one to four days after infection. For COVID, symptoms can develop within anywhere from two to five days, all the way up to 14 days after infection.

If you have flu or COVID symptoms—especially if you’ve recently been in contact with someone who has it—call your health care provider or take a rapid home COVID test that will quickly tell you if you're infected. Home flu tests and combination flu/COVID home tests are also available at most pharmacies. The earlier you can confirm a diagnosis, the earlier you can start treatment and distance yourself from others.

Infectious phase

• Flu: With influenza, you're most contagious during the first three days of symptomatic illness—but some people may be contagious for longer periods.
• COVID: If you’re infected with COVID, you can begin infecting others one to two days before symptoms start. You're usually considered to be contagious for roughly 8-10 days after your symptoms began.

Complications

• Flu: Flu complications are more likely in certain groups, including those age 65 or older and people with certain chronic conditions. Pneumonia is one example of a serious complication, as well as inflammation of the heart (myocarditis) and brain (encephalitis). Flu can also worsen chronic medical conditions (e.g., asthma).
• COVID: In severe cases, COVID can cause Acute Respiratory Distress Syndrome (ARDS), where the lungs cannot provide enough oxygen to the rest of the body. This often requires hospitalization and, in severe cases, mechanical ventilation. The virus can also lead to pneumonia, a condition in which the air sacs in the lungs become inflamed.

Other common complications of COVID include blood clots, septic shock, organic damage or failure, and secondary bacterial infections (e.g., bacterial pneumonia).

A condition called long COVID can also develop in people with previous infection(s). With long COVID, debilitating symptoms may continue or emerge many months after the acute infection. Fortunately, long COVID rates appear to be stabilizing, according to KFF. As of March 2024, roughly 17 million adults (17 million people) reported they have this condition.¹

Treatment

With both flu and COVID, early treatment is vital to reducing the severity of symptoms and preventing complications—especially in high-risk groups like older adults.

• Flu: Antiviral medications like Tamiflu (oseltamivir), Relenza (zanamivir), and Xofluza (baloxavir marboxil) can reduce the severity and duration of flu symptoms if taken within one to days after symptoms start. These medications can help prevent serious complications, especially in older adults or people with underlying health conditions.
• COVID: Paxlovid (nirmatrelvir and ritonavir) and Molnupiravir (Lagevrio) are oral antiviral treatments for COVID that can reduce the severity of illness and prevent hospitalization, but must be started within five days of symptom onset. Remdesivir is a three-day antiviral treatment given via IV in a hospital setting for severe cases of COVID. Corticosteroids may also be used to help reduce inflammation in the lungs.

For both the flu and COVID, managing symptoms is important. Getting enough rest, drinking plenty of fluids, and eating well will go a long way in your recovery. If you’re having fever or aches and pains, over-the-counter (OTC) medications like ibuprofen or acetaminophen can offer temporary relief.

How can I protect myself from flu and COVID this winter?

Since older adults are more likely to experience complications from the flu and COVID, it’s essential to be proactive. Here are some ways to stay safe and healthy this season:

• Get vaccinated: The number-one way to prevent both flu and COVID is to stay up to date with your flu shot and COVID vaccine. The Centers for Disease Control and Prevention (CDC) recommends a 2024-2025 COVID vaccine for most people age 18 and older to protect against severe illness, hospitalization, and death (a reformulated 2025-2026 vaccine is coming in the fall of 2025). Those who are moderately or severely immunocompromised may benefit from an extra COVID vaccine, starting at least two months after their last updated shot—if their provider recommends it. For the 2025-2026 season, CDC recommends a flu shot for everyone age six months and older, with rare exceptions. If you’re 65 or older, at higher risk for serious illness, or have never had a COVID shot, it’s especially important to get vaccinated. While vaccines may reduce the risk of getting infected, they also make symptoms milder if you do get infected and reduce hospitalizations and death. Can you get your flu and COVID vaccines at the same time? Yes! But if you tend to get soreness at the injection site or other side effects, you may want to schedule separate appointments.
• Practice good hygiene: “Wash your hands” sounds like common sense, but it bears repeating. Make sure to wash yours often with soap and water, avoid touching your face, and sanitize high-touch surfaces regularly (e.g., door handles and appliance knobs in your home).
• Wear a mask where it counts: During peak flu season or when COVID and flu rates are high in your community, it’s a good idea to wear a well-fitting mask in crowded or indoor public settings. This can help prevent you from getting sick—and prevent you from spreading it to others if you’re infected and do not yet know it.
• If you’re feeling ill, stay home and rest: When you're under the weather—whether it's from the flu, COVID, or a common cold—your body is hard at work fighting off an infection. By staying home, you give yourself the rest you need to make a full recovery, while also preventing the spread of illness to other people.

Learn more about vaccines for older adults

Did you know immunizations are important at every age and stage? Getting routine preventive vaccinations in adulthood helps us maintain immunity from childhood vaccines that lose effectiveness over time. More importantly, it can help us avoid seasonal illnesses like the flu, COVID, shingles, RSV, and emerging diseases. Visit NCOA’s Vaccine Information and Resources page to get the facts on recommended vaccines for older adults.

Sources

1. KFF. Long COVID Rates Appear to be Stabilizing, Affecting About 1 in 10 Adults Who Have Had COVID. April 9, 2024. Found on the internet at https://www.kff.org/covid-19/long-covid-rates-appear-to-be-stabilizing-affecting-about-1-in-10-adults-who-have-had-covid/ ​​​​​​​