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An Invisible Threat

Once scientists had identified the flu virus, the next step

was to discover how it got inside cells and caused disease.
They were then able to understand how the virus spread.

Virus Invasion

When a virus invades a body, it seeks out cells and moves inside them.
Once inside a cell, a virus uses the cell to replicate, or make copies of
itself, so it can spread rapidly to other cells throughout the body.
Once the virus has done this, it can spread to other people.

Virus All Around

When someone coughs
or sneezes, viruses from
their mouth and nose
can travel through the

air around them, where
other people breathe
them in. Traces of the

flu virus can also be left
on surfaces, such as a
phone or doorknob,
when someone who

is sick touches them.
When another person
touches those objects
The flu spreads from and then their eyes,
person to person nose, or mouth, the virus
through actions such
as sneezing, coughing, enters their body and
and touching. makes them sick.

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