Vaccinations: part 2
A population without an immunisation programme against disease
is vulnerable to all the effects of that disease.
Many people will suffer, some die, some may be left with permanent disability.
Even if there is an immunisation programme,
if enough people are left unvaccinated,
the germ can still infect those who aren't protected.
When enough people are immunised,
it is very hard for the germ to find anyone who isn't vaccinated.
Because of this herd immunity, non-immunised people are protected.
They are protected both from catching the disease
and suffering any permanent disability.
When enough people are protected,
it is possible for some diseases to disappear forever,
as happened with smallpox,
and will happen with polio and eventually measles.
When this happens, the World Health Organisation
can certify the world to be free of that disease
and vaccination for the disease will no longer be needed.