Influenza vs COVID-19: Key Differences in Symptoms, Spread, and Risk

When you feel sick with a fever, cough, and body aches, it’s hard to tell if it’s the influenza, a seasonal viral infection that circulates every year and affects millions globally or COVID-19, a disease caused by the SARS-CoV-2 virus that emerged in 2019 and changed global health systems. Both attack your respiratory system, but they’re not the same virus, and the differences matter—especially when deciding whether to stay home, get tested, or rush to the ER.

The flu, a common respiratory illness caused by influenza A or B viruses usually hits fast. Symptoms like fever, chills, sore throat, and muscle pain show up within 1 to 4 days after exposure. Most people feel better in a week. COVID-19, triggered by the SARS-CoV-2 virus, can take longer to show up—up to 5 days on average, sometimes even 14. It also brings unique signs like loss of taste or smell, which are rare with the flu. While both can cause pneumonia and hospitalization, COVID-19 has a higher chance of leading to long-term issues like brain fog, fatigue, or heart inflammation, even in young, healthy people.

Transmission is another big difference. The flu spreads mostly through big droplets when someone coughs or sneezes. COVID-19 does that too, but it also hangs in the air as tiny particles, especially indoors with poor ventilation. That’s why one infected person can spread COVID-19 to many more people than they would the flu. And while flu vaccines are updated yearly based on what’s circulating, COVID-19 vaccines had to be developed from scratch and keep evolving as new variants appear.

Who’s most at risk? Older adults and people with chronic conditions like diabetes or heart disease are vulnerable to both. But COVID-19 hits harder on younger adults without pre-existing conditions than the flu ever did. Pregnant women, children, and immunocompromised people need extra caution with both, but the consequences of misidentifying one for the other can be serious—like delaying treatment or exposing others unknowingly.

Testing is the only way to be sure. A rapid flu test or PCR can tell you which virus you’re dealing with. And while over-the-counter meds help with symptoms for both, antivirals like oseltamivir (Tamiflu) work for flu, and Paxlovid is prescribed for high-risk COVID-19 cases. Ignoring the difference means missing the right treatment.

Below, you’ll find real-world guides on how to spot the signs early, avoid dangerous mistakes with medications, and protect yourself and others—whether you’re managing symptoms at home, checking your medicine cabinet, or navigating prescription refills during an outbreak. These aren’t theoretical tips. They’re from people who’ve been there.