Flu vs COVID-19: Both can cause fever, cough, sore throat, tiredness and body aches. Symptoms alone cannot reliably tell them apart. Testing can identify the infection and help guide treatment, especially if you have a higher risk of becoming seriously ill.
Influenza viruses cause flu. SARS-CoV-2 causes COVID-19. Because the infections require different antiviral medicines, guessing from a symptom list can delay the right assessment.
This article provides general health information and does not replace individual medical advice.
- Flu vs COVID symptoms
- Testing and negative results
- Can you have both?
- When to seek advice early
- Treatment differences
- Emergency warning signs
- Protecting others
- Persistent symptoms
- Common questions
Flu vs COVID symptoms: What overlaps?
A comparison table can show why the distinction is difficult. The presence or absence of one symptom does not confirm either illness.
| Symptom or clue | What it tells you |
|---|---|
| Fever or chills | Can occur with either illness; not everyone with flu has a fever |
| Cough and sore throat | Possible with both infections |
| Congestion or runny nose | Does not establish that the illness is a cold |
| Body aches, headache and fatigue | Can overlap substantially |
| Vomiting or diarrhea | Possible with COVID-19 and flu; digestive symptoms with flu are more common in children |
| New change in taste or smell | Can occur with COVID-19; its absence does not rule out infection |
COVID-19 symptoms can vary with viral variants and vaccination status. Flu often starts suddenly, but onset alone cannot separate it from COVID-19.
Sources: CDC COVID-19 symptoms and CDC flu symptoms. Our influenza symptoms guide explains the main flu signs in more detail.
Flu and COVID testing: What should you know?
Some tests check for influenza and SARS-CoV-2 together. Others detect only one infection. Read the packaging or ask the testing service which viruses the test covers.
Tests also differ in sensitivity. Molecular tests, including PCR tests, are generally more sensitive than rapid antigen tests. A clinician can advise which test is appropriate based on symptoms, timing and your medical history.
Sources: CDC flu testing and CDC COVID-19 testing.
What if a COVID antigen test is negative?
A single negative antigen result does not rule out COVID-19. CDC cites FDA recommendations for repeat testing 48 hours apart: at least two tests for someone with symptoms, or three for someone without symptoms. A molecular test may be another option.
Follow the manufacturer's instructions. If you have symptoms and higher-risk conditions, contact a clinician promptly while arranging appropriate testing. Do not wait through repeat tests before asking about time-sensitive treatment.
Source: CDC guidance on interpreting COVID-19 tests.
What if a rapid flu test is negative?
A negative rapid flu test can miss influenza. It does not automatically mean you have COVID-19, either. A clinician considers the result alongside symptoms and may use a more sensitive test or make a clinical assessment.
Source: CDC guidance on flu test limitations.
Can you have flu and COVID-19 at the same time?
Yes. Co-infection is possible. A positive result for one virus does not exclude the other. Combined testing may help identify both when that information would affect care.
Tell your clinician about all test results and any deterioration. Do not assume a second infection is impossible because you already have one diagnosis.
Source: CDC clinical guidance on co-circulating flu and COVID-19.
Who should seek medical advice promptly?
Older adults and people with certain chronic conditions or weakened immune systems may face greater risk from either infection. Pregnancy also makes early assessment important.
The risk groups are not identical. Children younger than 5, especially those younger than 2, are at increased risk of flu complications. A person's COVID-19 risk also depends on factors including age, underlying conditions and vaccination status.
If you belong to a higher-risk group, seek advice even when symptoms seem mild. Give the clinician your symptom start date, relevant conditions, current medicines and test results. Treatment options depend partly on how much time has passed.
Sources: CDC flu risk groups and CDC COVID-19 risk factors.
How do flu and COVID-19 treatments differ?
The antiviral medicines used for flu and COVID-19 are different. Treatment eligibility, timing and medication interactions need an individual assessment. Do not use someone else's prescription or assume one antiviral treats both infections.
Flu treatment timing
Flu antivirals work best when started within two days of symptoms beginning. Later treatment may still help people who are very ill or at higher risk. CDC recommends prompt treatment assessment for these groups.
For priority patients with suspected flu, clinicians should not delay antiviral treatment while waiting for laboratory confirmation.
Sources: CDC flu treatment and CDC clinical antiviral recommendations. See our flu treatment and home care guide.
COVID-19 treatment timing
For eligible higher-risk patients, COVID-19 treatment must start early. Nirmatrelvir with ritonavir, commonly known as Paxlovid, must begin within five days of symptoms starting. A three-day outpatient remdesivir course must begin within seven days.
These windows describe particular treatments, not a reason to wait. Contact a clinician as soon as symptoms develop if you are at higher risk. CDC notes that a positive test is not always required before treatment can begin.
Some COVID-19 medicines interact with other drugs. Share your full medicine list, including supplements, so a clinician or pharmacist can assess safety. Availability and eligibility vary by location.
Source: CDC COVID-19 treatment options.
When should you seek emergency care?
Seek emergency medical help for difficulty breathing, persistent chest pain or pressure, new confusion, or difficulty waking or staying awake. A pale, gray or blue appearance of lips, skin or nail beds can also be a warning sign, depending on skin tone.
For children, signs such as struggling to breathe, ribs pulling inward with breaths, poor alertness or dehydration need urgent attention. Any fever in a baby younger than 12 weeks requires immediate assessment.
These examples are not exhaustive. Seek prompt assessment for severe or concerning symptoms, or if illness improves and then worsens. Do not wait to identify the virus before getting emergency help.
Sources: CDC COVID-19 warning signs and CDC flu warning signs.
How can you protect others while sick?
Stay home and away from others while ill. Under CDC general community guidance, normal activities can resume after at least 24 hours of both overall symptom improvement and no fever without fever-reducing medicine.
For the next five days, use added precautions such as cleaner air, good hygiene, a well-fitted mask and distancing where appropriate. You may still be able to spread infection while feeling better.
If fever returns or symptoms worsen after resuming activities, stay home again. Follow local requirements, school and workplace policies, and any infection-specific advice. Healthcare settings have separate guidance.
Source: CDC precautions when sick.
For prevention beyond the current illness, discuss vaccination recommendations appropriate to your age and circumstances. Cleaner indoor air and hygiene also help reduce respiratory infection risk.
Source: CDC respiratory illness prevention.
What if symptoms persist?
Persistent tiredness or cough cannot retrospectively establish which virus caused an illness. Discuss symptoms that interfere with daily life, fail to improve or change unexpectedly with a healthcare professional.
Long COVID can occur after SARS-CoV-2 infection, including after mild illness. It can involve ongoing or recurring symptoms and requires clinical assessment. A lingering symptom alone is not a diagnosis, and there is no single laboratory test that confirms Long COVID.
Source: CDC Long COVID basics.
Common questions about flu vs COVID
Can you tell flu from COVID by symptoms alone?
No. The overlap is too substantial for a symptom checklist to reliably distinguish them. Testing can clarify the cause.
Does a negative COVID test mean you have flu?
No. An antigen test may miss COVID-19, and other illnesses can produce similar symptoms. Follow repeat-testing instructions and seek advice when needed.
Does a flu antiviral also treat COVID-19?
No. Influenza antivirals target flu. COVID-19 has different treatment options selected according to eligibility and timing.
Sources: CDC flu and COVID-19 comparison, CDC COVID-19 testing and CDC COVID-19 treatment.
If you are also considering a common cold, read our flu vs cold comparison.