1. Influenza A
Influenza A is the most common and most serious type.
- Causes seasonal flu outbreaks every year
- Can lead to flu pandemics
- Infects humans and animals (such as birds and pigs)
- Subtypes are named by proteins on the virus surface, such as H1N1 or H3N2
Influenza A is responsible for most hospitalisations and deaths related to flu, especially in older adults, young children, and people with long-term health conditions.
2. Influenza B
Influenza B usually causes milder illness than type A, but it can still be serious.
- Affects humans only
- Does not cause pandemics
- Often affects children and teenagers
- Circulates mainly during the flu season
There are two main strains: B/Victoria and B/Yamagata.
3. Influenza C
Influenza C causes very mild illness or no symptoms at all.
- Does not cause outbreaks or epidemics
- Usually affects young children
- Symptoms are similar to a mild cold
Because illness is mild, influenza C is not included in routine flu vaccines.
Key Differences at a Glance
| Type | Severity | Who it affects | Pandemics |
|---|---|---|---|
| Influenza A | Moderate to severe | Humans & animals | Yes |
| Influenza B | Mild to moderate | Humans only | No |
| Influenza C | Very mild | Mostly children | No |
Summary
- Influenza A: most serious, causes epidemics and pandemics
- Influenza B: seasonal, usually milder, mainly affects humans
- Influenza C: mild, cold-like illness
Seasonal flu vaccines protect against influenza A and B, which are responsible for most flu-related illness.
