What causes influenza?
Influenza is caused by a virus. There are four types of influenza virus; A, B, C and D.
There are then various subtypes of these four types. Human influenza A and B viruses are the cause of the seasonal epidemics of disease (known as the flu season) almost every winter. Influenza A viruses are the only influenza viruses known to cause flu pandemics, i.e., global epidemics of flu disease.
A pandemic can occur when a new and very different influenza A virus emerges that both infects people and has the ability to spread efficiently between people.
Covid-19 is not an influenza virus. It is a coronavirus which is a type of virus. Coronaviruses (CoV) are a family of viruses including but not limited to SARS-CoV and MERS-CoV.
How do new viral strains emerge?
New influenza viral strains constantly arise from two mechanisms that alter the genetic code of a virus. These mechanisms are known as genetic drift and genetic shift. Genetic drifts are small changes in genetic material called point-mutations which can occur in a single virus strain. Genetic shifts is when the genetic material of different strains of influenza viruses mix and form new combinations.
How does the flu vaccine work?
The seasonal flu vaccine protects against the influenza viruses that research indicates will be most common during the upcoming season.
Most flu vaccines protect against four different flu viruses (“quadrivalent”); two influenza A viruses, and two influenza B viruses. Getting the flu vaccine can protect against flu viruses that are similar to the viruses used to make the vaccine. But the flu vaccines will not protect against infection and illness caused by other viruses, such as COVID-19, that also can cause influenza-like symptoms.
Some of the theories are:
- Southeast Asia contains more than half of the global population. Larger populations should sustain larger virus populations, and in the absence of other reasons, they should contribute to a larger proportion of strains that happen to spread globally.
- Birth rates have historically been higher in South East Asia than in most temperate populations. High birth rates influence the susceptibility of the population due to increased percentage of non-immune individuals resulting in decreased immunity to a virus strain and thereby allowing for genetic change.
- Strong trade connections between Europe, North American and Australasia exports new viruses to other countries.