Winter respiratory viruses and seasonal respiratory illnesses continue to circulate together with COVID-19, so the coronavirus is difficult to differentiate between coronavirus and influenza.
The coronavirus and the flu have many symptoms, including fever, cough, fatigue, sore throat and body aches and the infection can be difficult to diagnose purely on the basis of symptoms. Infectious disease experts say while there are similarities, there are also differences in what it means to be tested, how one should know if they should seek medical attention or not, and in what case to be advised to go to the doctor.
Doctors explain that COVID-19 and influenza are contagious viral respiratory diseases but are caused by different viruses. COVID-19 is caused by the SARS-CoV-2 virus, while seasonal flu is due to influenza A or influenza B viruses. Both respiratory droplets and aerosols are spread primarily when an infected person coughs, sneezes, talks, or breathes close to others.
The hardest part is that the early symptoms of both illnesses often overlap. People with either virus may have fever, chills, headache and muscle pain, fatigue, sore throat, nasal congestion and cough. Children may also be experiencing vomiting or diarrhea, and some people may be sick, especially children. Because these symptoms are so similar, healthcare professionals say it is often impossible to determine if someone has the infection based on symptoms alone.
However, there are subtle differences. Influenza often starts abruptly, and people often feel well one moment and then develop fever, body aches, chills and exhaustion within a couple of hours. COVID-19 can also occur abruptly but it may develop more slowly over one or two days. While fever and cough are some of the most common symptoms of COVID-19, some patients may have milder or no symptoms at all.
Dr. Williams said that loss of smell or taste was once considered a signature sign for COVID-19, especially for earlier waves of the pandemic. While this symptom can still show up, it is now less common for the newer variants and therefore it is no longer considered a reliable way to distinguish between COVID-19 and influenza.
Another difference, of course, is in the potential complications. While both illnesses do cause pneumonia and respiratory disease, COVID-19 has been associated with a higher risk of blood clotting disorders, prolonged fatigue and post-viral symptoms often referred to as "Long COVID." Influenza, on the other hand, might cause bacterial pneumonia, sinus infections or worsening of chronic medical conditions, particularly among older adults.
Medical experts say the most reliable way to determine whether someone has COVID-19 or influenza is through laboratory testing. Rapid antigen tests are commonly used to detect COVID-19, and during flu season healthcare providers may suggest testing for influenza. In some healthcare settings, combined tests are available that can detect both viruses from a single sample.
Treatment is also different for the two illnesses. Most people with mild COVID-19 or influenza recover at home with adequate rest, hydration, nutrition and medications to relieve fever or pain as recommended by a healthcare professional. Antiviral medication is available for influenza and is most effective when started within 48 hours of symptom onset. Some antiviral treatment for COVID-19 in patients at higher risk of having severe disease can also be prescribed.
Health professionals recommend getting quick medical help if symptoms are severe. Common signs include difficulty breathing, persistent chest pain, confusion, inability to stay awake, bluish lips or face; symptoms that get worse after initially getting better. If they are elderly, pregnant, immunocompromised, or have chronic diseases such as diabetes, heart disease, kidney disease, or lung disease, they should see a doctor early if they start to show symptoms.
Preventive measures are still effective against both viruses. Regular handwashing, covering coughs and sneezes, staying home when sick, ensuring good indoor ventilation, and avoiding contact with those who are vulnerable when sick can help prevent transmission. Vaccination is still one of the most effective ways to minimize the risk of severe illness, hospitalization and death from COVID-19 and seasonal influenza. Doctors recommend that eligible individuals stay up to date with recommended vaccines based on public health guidance.
Medical professionals also recommend against self-diagnosing based solely on symptoms or information circulating on social media. COVID-19, influenza, and other respiratory viruses such as RSV can present in similar ways, so proper medical evaluation is key, especially if symptoms are severe or persistent.
As respiratory viruses continue to spread throughout the year, awareness and timely medical care are crucial. COVID-19 and influenza are not identical, and understanding their differences and seeking appropriate testing when necessary can help ensure early treatment, reduce transmission, and protect those most vulnerable to serious illness.
