Type A flu causes symptoms that come on suddenly, often within hours: fever, body aches, chills, cough, sore throat, headache, and deep fatigue. Symptoms typically appear about two days after exposure, though the incubation period can range from one to four days. Most people recover within a few days to less than two weeks.
Core Symptoms of Type A Flu
The hallmark of influenza A is how fast it hits. One moment you feel fine, and a few hours later you’re flat on the couch with a fever and aching muscles. The full list of symptoms includes:
- Fever or chills: Fever is common and typically lasts three to four days. Not everyone with the flu develops a fever, but most do.
- Cough: Usually dry and persistent, often one of the last symptoms to resolve.
- Sore throat
- Runny or stuffy nose
- Muscle or body aches: Often described as a deep, all-over soreness that makes it hard to get comfortable.
- Headache
- Fatigue: This isn’t ordinary tiredness. Flu-related exhaustion can leave you unable to manage basic daily tasks and may linger after other symptoms improve.
Some people, particularly children, also experience vomiting and diarrhea, though these are more common in stomach bugs than in influenza.
How Symptoms Progress Over Time
The first one to three days are typically the worst. Fever, chills, and body aches dominate early on, and most people feel too wiped out to do much of anything. By day three or four, fever usually breaks, and the intense body aches start to ease.
What often lingers is the cough and fatigue. Even after the fever is gone and you’re generally feeling better, a dry cough can stick around for a week or more. The fatigue can take even longer to fully resolve. It’s common to feel drained for one to two weeks after the acute illness passes, which catches people off guard when they assume the worst is over once the fever drops.
How Flu Feels Different From a Cold
The biggest difference is intensity and speed. Colds creep in gradually over a day or two, starting with a scratchy throat or sniffles. The flu announces itself all at once with fever, aches, and exhaustion. Colds are generally milder overall. You might feel lousy with a cold, but you can usually still function. The flu tends to put you in bed.
Nasal congestion is also a useful clue. People with colds are more likely to have a runny or stuffy nose as a primary complaint. With the flu, congestion may be present, but it takes a backseat to the systemic symptoms like fever, muscle pain, and fatigue. Colds also rarely lead to serious complications like pneumonia or hospitalization, while the flu can.
Type A vs. Type B: Is There a Difference?
In terms of what you actually feel, not much. A CDC study comparing hospitalized adults with influenza A and influenza B found no significant difference in disease severity. Length of hospital stay, the proportion of patients admitted to intensive care, and death rates were comparable between the two types. The symptoms are essentially the same: fever, cough, aches, fatigue.
The real distinction between type A and type B is epidemiological, not experiential. Type A is responsible for flu pandemics because it mutates more rapidly and can jump between animals and humans. Type B circulates only in humans and tends to cause smaller outbreaks. But if you’re lying in bed with the flu, your body doesn’t care which letter is attached to it.
When Symptoms Signal Something More Serious
Most people recover from type A flu without complications. But the illness can turn dangerous, particularly in certain groups. Adults 65 and older, children younger than 2, pregnant women, and people with chronic conditions like asthma, diabetes, heart disease, or weakened immune systems face a higher risk of serious complications. Children under 6 months old have the highest hospitalization and death rates among pediatric age groups.
Warning signs that the flu is becoming more than a routine illness include difficulty breathing or shortness of breath, chest pain or pressure, confusion or sudden dizziness, severe or persistent vomiting, and symptoms that improve but then return with worsening fever and cough. That last pattern, feeling better and then getting worse again, can signal a secondary bacterial infection like pneumonia developing on top of the original flu.
In children, watch for fast or labored breathing, bluish skin or lips, severe irritability (where the child doesn’t want to be held), and not drinking enough fluids. Dehydration is a particular concern in young children with high fevers.
Contagiousness and Timing
You can spread the flu before you even know you’re sick. Most people become contagious about one day before symptoms appear and remain contagious for five to seven days after getting sick. Children and people with weakened immune systems may be contagious for even longer. This pre-symptomatic spread is one reason flu moves through households and workplaces so efficiently: by the time you realize you have it, you’ve likely already exposed the people around you.