2. What is the virus that
causes flu? Why doesn't the
body produce permanent
immunity against that virus?
How does the vaccine against
flu work?

Gap-fill exercise

Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!
Flu is a disease by the influenza
virus, highly mutant DNA virus.
to the high mutation of the virus,
that many different strains, flu
presents epidemic features in
populations and people may
several flu episodes during
(the immune response made
previous infections is not in
future infections).

The against flu is a
made of attenuated virus three
different strains. Each the WHO
(World Health ) researches
and determines which the strains
that should the vaccine. This is
strategy to face the mutation
rate of the .