the flu virus mutates easily so every year there are new strains of virus that your immune system doesnt recognise
no effective treatment against viruses at all
Epidemic (one country) and pandemic (across several countries)

IMMUNITY

every cell has unique proteins on its surface called antigens. Antigens on micro-organisms are different to the ones on your own cells- the immune system recognises this- wbc's then make antibodies and destroy the pathogens- your white blood cells remember the right antibody needed for a particular pathogen- if you meet the same pathogen again, they can make the same antibody very quickly- immunity
so first time you meet a pathogen you feel ill, second time you dont (pathogens killed before you have time to)
VACCINATION- protected against serious diseases by immunisation or vaccination- given a vaccine made of a deadened for of the disease causing micro-organism- triggers your body's natural immune response to invading pathogens- wbc's develop the right antibodies against the pathogen without you getting ill so, if you meet the live pathogens, can make the antibodies faster and you are not affected.
Use vaccines against bacterial and viral infections- can wipe out diseases if a large population is immunized (smallpox)
very small risk within vaccines- but outweigh the consequences of not having- some people have forgotten this now serious diseases are becoming less frequent
whooping cough scare story- extreme consequences
scientists constantly looking for new antibiotics due to antibiotic- restistant strain issue:

GCSE Core Biology Revision 1