Callista wrote:
Vaccines are not 100% effective; but that's not the same as "doesn't work". What's typical is something like,
With vaccine: 20% chance of catching illness after exposure
Without vaccine: .01% chance of catching illness after exposure
That kind of thing. There's always a chance your body didn't properly develop immunity, and you'll get the illness--though usually a mild version of it. Obviously you aren't protected against what you weren't vaccinated for, which is important with viruses that tend to mutate (like the flu virus) or when there are many causes of a single illness (meningitis or, yes, pneumonia); and immunity can wear off, as with tetanus which requires regular re-exposure to the vaccine to keep up immunity.
This is an argument FOR getting vaccinated!(BTW, you switched the statistics) If someone gets vaccinated, it means there is a 1 in 99.99 chance they MIGHT get infected IF exposed! There is ALSO a better chance that IF they get infected, the case will be more mild and less contagious!
So with 1000 people going from a civilized area to an undeveloped country, the chances are that only ONE person has a SLIGHT chance of spreading the disease. The chances of that causing a mild epidemic are practically ZERO! They are probably like .0001%! If they WEREN'T vaccinated, about 200 could come back with a FULL case! The chances of THEM starting an epidemic could be about 100%!
BTW People that haven't been vaccinated in a long time, were vaccinated with another strain, are undernourished, have another disease, are tired, etc.... Are FAR more likely to catch the virus. Vaccinations were NEVER 100%, but they DID wipe out polio and smallpox!! !! !! !!