DW: Since this going around my house, thought I'd share.
Flu viruses are divided into four types: A, B, C, and D. During flu season (October through May), you’ll mostly hear about flu A and flu B. Flu C viruses only cause mild illness in humans and are not linked to large outbreaks. Flu D viruses do not appear to infect humans at all and are mainly found in cattle.
Now that we know there are two main types of flu viruses that affect humans, you may be wondering: Which flu is worse, A or B? Answering that question starts with learning more about their differences and how they affect us.
What is the difference between influenza A and B?
While flu A and flu B both cause seasonal flu, there are several differences in terms of their structure, behavior, and who they impact.
Flu A is the more common of the two main flu types, making up about 75% of all cases.2 This type can infect not only humans, but also animals such as birds and pigs.
The Flu A virus is divided into subtypes based on two proteins found on its surface. These subtypes can combine in different ways to form various strains of flu A—like H1N1 and H3N2, which are the two main strains that currently affect humans. This versatility allows flu A to mutate and change more frequently, making it harder for our immune system to recognize and fight off.
Since flu A can infect multiple species and mutate more easily, it’s often the culprit behind widespread flu outbreaks and pandemics. This includes the 2009 H1N1 pandemic (also known as “swine flu”), which affected millions of people around the globe. Every year leading up to flu season, health experts keep a close eye on flu A strains. This scrutiny enables scientists to develop a vaccine that effectively targets the strains most likely to be circulating.
Flu B only affects humans. It’s less common, making up roughly 25% of all flu cases, and less likely to cause pandemics (although it can still cause outbreaks).
Flu B viruses are broken down into two main lineages: the B/Yamagata and B/Victoria lineages. These two strains can still cause seasonal flu epidemics, but they’re less likely to mutate. Also, they don’t change as much from year to year like flu A strains do.
Another difference between flu A and flu B timing. Flu B tends to circulate later in the flu season compared to A, often peaking in the spring.
Are the symptoms of flu A and B different?
Flu A and B share similar symptoms. The most common symptoms of flu include:
- Fever (100-102 °) and/or chills
- Headache
- Muscle or body aches
- Weakness/fatigue
- Extreme exhaustion
Other flu symptoms may include stuffy/runny nose, sneezing, and sore throat.
Which flu is worse, A or B?
Flu A tends to be more aggressive and cause more severe symptoms compared to flu B. It’s more common in adults. In contrast, flu B is more common in children. While it typically causes mild illness, type B can be more severe in children under age 5 and older adults.
Generally speaking, older adults are more likely to experience complications from both types of flu viruses. This is because our immune system is not as efficient at fighting off viruses as we age.
Can you have flu A and B at the same time?
Yes, it's possible to have flu A and flu B and even other respiratory illnesses (like COVID) at the same time. However, it’s not yet understood how common this is. You can also contract flu B after getting flu A (or vice versa), since having the antibodies from one type does not protect you from getting infected with the other.
https://www.ncoa.org/article/whats-the-difference-between-flu-a-and-flu-b/