Seasonal influenza, commonly known as the flu, affects millions of people worldwide each year. While many associate “the flu” with a single illness, there are actually different types of influenza viruses, namely Flu A and Flu B. Understanding the differences between these two can help you recognize symptoms early, seek the right treatment, and reduce the risk of complications. In this blog, we will break down the differences between Flu A vs Flu B, including their symptoms, treatments, duration, and prevention tips.
According to the World Health Organization (WHO), “Influenza is an acute respiratory infection caused by influenza viruses, which circulate worldwide and can affect people in any age group.”
The Ministry of Health Singapore (MOH) states that “Influenza is a highly contagious viral infection of the respiratory tract, causing fever, sore throat, cough, body aches and fatigue.”
Influenza A is the most common strain of the flu virus, accounting for approximately 75% of all flu cases, according to the Centers for Disease Control and Prevention (CDC). This virus can infect humans, birds, and some mammals like pigs, allowing it to mutate and spread more easily. Adults are generally more likely to contract Flu A than Flu B.
Because Flu A mutates frequently, it increases the chance of reinfection, as the immune system may not always recognize the virus. This mutation capability also explains why Flu A is often responsible for larger outbreaks and even pandemics. It tends to circulate mostly in the fall and winter seasons.
Influenza B causes about 25% of flu cases and infects only humans, making it less prone to mutation compared to Flu A. As a result, the immune system is often better able to recognize and combat the virus, reducing the likelihood of frequent reinfection.
Children are more susceptible to Flu B, and while it can still cause severe illness, it is less likely to cause widespread outbreaks. Flu B typically circulates later in the flu season, often peaking in the spring.
According to Singapore’s Ministry of Health (MOH), influenza occurs throughout the year in tropical regions like Singapore, with typically two peaks, usually between December to February and May to July. Both Influenza A and B are regularly found in local circulation.
The flu is caused by influenza viruses, a group of contagious respiratory pathogens that infect the nose, throat, and lungs. These viruses spread easily from person to person, especially in crowded or enclosed environments.
There are four main types of influenza viruses: A, B, C, and D, but only influenza A and B are responsible for seasonal flu outbreaks in humans.
Influenza viruses spread through respiratory droplets expelled when an infected person coughs, sneezes, talks, or even breathes in close contact. You can catch the flu by:
A person with the flu is typically most contagious in the first 3–4 days after symptoms begin, but they can spread the virus as early as 1 day before symptoms appear and up to 7 days afterward.
Certain factors increase your risk of getting the flu or experiencing more severe symptoms:
The Ministry of Health in Singapore emphasizes that individuals with flu-like symptoms should stay home, wear a mask, and avoid public places to reduce the risk of transmission. Children who are unwell should refrain from attending school or childcare facilities, and the elderly or chronically ill should seek early medical attention due to the higher risk of complications. Need instant medical advice? Book a teleconsultation with a licensed doctor anytime via the MaNaDr App and get access to quality healthcare 24/7 right from home.
Both Influenza A (Flu A) and Influenza B (Flu B) are responsible for seasonal flu epidemics, but they differ in terms of origin, mutation rate, severity, and outbreak potential.
| Features | Flu A | Flu B |
| Hosts | Infects both humans and animals | Infects only humans |
| Mutation Rate | High (frequently changes, leading to new strains) | Slower mutation rate |
| Pandemic Potential | High – can lead to global outbreaks (e.g. H1N1) | Low – causes localized outbreaks |
| Subtypes | Many subtypes (e.g. H1N1, H3N2) | Two main lineages (B/Yamagata, B/Victoria) |
| Severity | Often more severe, especially in high-risk groups | Usually milder but still serious |
| Seasonality | Peaks typically seen between Dec–Feb in Singapore | Circulates seasonally, also peaks in similar periods |
Flu A is generally considered more dangerous than Flu B for several reasons:
That said, Flu B should not be underestimated. It can still cause severe illness, especially in children, and has led to serious complications and hospitalizations.
Flu symptoms often appear suddenly and can vary in intensity depending on the type of influenza virus. While the symptoms largely overlap, there are subtle differences in severity and timing that may help you identify which type you might have.
Regardless of the type, most people with the flu experience some combination of the following symptoms:
Influenza A is typically more aggressive and can hit harder, especially in adults and those with weakened immune systems. Key signs include:
Because Flu A tends to mutate frequently, symptoms can be more severe and lead to complications like pneumonia.
Influenza B generally causes a milder illness, though it can still be serious, especially in children and the elderly. Symptoms may include:
While Flu B doesn’t mutate as quickly, it can still lead to hospitalization in high-risk individuals, especially during late winter or spring.
Note: It’s nearly impossible to know which type of flu you have based on symptoms alone. A rapid flu test or PCR test at a clinic or via teleconsultation is the only way to confirm whether it’s Type A or B.
Since flu A and flu B generally result in the same symptoms, the same treatment is usually used.
Flu is always caused by a virus, so treatment focuses on relieving symptoms and supporting the body’s recovery. Getting plenty of rest and staying hydrated is key. You can also take over-the-counter medications to reduce body aches and bring down any fever.
In more severe cases, a doctor may prescribe antiviral medication. When taken early, these medications can help reduce the severity of symptoms and shorten the duration of the illness.
If you catch the flu, whether it’s Flu A or Flu B, the most important thing is to take care of yourself and reduce the risk of spreading the virus to others.
Here are some general steps to follow:
Preventing the flu starts with taking proactive steps to protect yourself and others. Here are some simple yet effective ways to lower your risk:
By following these simple practices, you can reduce your chances of getting the flu and help protect those around you.
Whether it’s Flu A or Flu B, both types can lead to uncomfortable symptoms and potential complications if not managed properly. The best defense is early detection, proper care, and prevention through vaccination and good hygiene habits.
If you’re experiencing any flu-like symptoms, you should consult a doctor early. You can book a teleconsultation instantly via the MaNaDr App and connect with quality doctors 24/7 from the comfort of your home.
