Causes of Flu
The causes of flu are rooted in infection by influenza viruses, which spread through droplets released when an infected person coughs, sneezes, or talks. Flu is highly contagious and can also spread via contact with contaminated surfaces, especially in crowded places like schools, offices, and public transport.
Influenza Virus Types
There are four main types of influenza viruses:
- Influenza A – the most common and severe; responsible for seasonal epidemics and pandemics
- Influenza B – less widespread than A but can still cause serious outbreaks
- Influenza C – causes mild illness and does not result in epidemics
- Influenza D – primarily affects cattle and is not known to infect humans
- Influenza A and B are the primary causes of seasonal flu in humans.
Mutation and Antigenic Drift
Influenza viruses constantly mutate, changing their surface proteins (haemagglutinin and neuraminidase). This process, called antigenic drift, allows the virus to evade the immune system, which is why previous exposure or vaccination may not provide full protection against future strains.
How It Spreads
Flu is mainly transmitted through:
Droplet spread, from coughing or sneezing
Surface contamination, where the virus lives for hours on doorknobs, mobile phones, and other shared items
Direct contact, such as shaking hands with an infected person
A person is most contagious in the first 3 to 5 days after symptoms begin but can spread the virus even before symptoms appear.
Seasonal Patterns
Flu outbreaks occur:
During winter months in most countries
With peaks between June and August in South Africa and between December and February in the northern hemisphere
In tropical regions, flu can circulate year-round with multiple peaks
Causes of Flu
The causes of flu are deeply connected to how easily the virus spreads and evolves. Understanding its transmission helps people take steps to protect themselves and those around them.
