Diseases like Smallpox and Polio now affect far fewer people because of widespread vaccination.

Vaccines contain inactive viruses or bacteria that stimulate your body's B and T immune

cells to produce antibodies, which then fight the disease.

When enough people get immunized, vaccines produce "herd immunity": when someone is sick,

the disease is contained by those who've had the vaccine, preventing it from spreading

further and getting to those who are most vulnerable.

But if only a few people are vaccinated, the disease spreads easily through the population

and outbreaks can occur.

In 1998, a paper in a major medical journal proposed a link between autism and the vaccination

for measles, mumps, and rubella.  The popular press (and some celebrities) fueled anxiety

about vaccinations based on this report.

Some vaccinations can have side effects, like soreness and fever.

But Autism is a complex neurobehavioral disorder that occurs with a spectrum of symptoms.  A

rise in prevalence may have more to do with changing diagnostic standards than other factors.

In fact, over a dozen studies have failed to find any connection between autism and

vaccines and that original paper was retracted amid allegations of fraud and conflicts of

interest.

Yet the actions of celebrities and the media can have a lasting effect: more than half

of Americans still suspect there's a link between vaccines and autism.  Call it a case

of "herd mentality."

The consequences can be serious: in Ireland, vaccinations dropped about 30%, resulting

in 1500 new cases of Measles and Mumps, including 3 deaths.

And in the U.S., states with lowered vaccination rates are currently experiencing outbreaks

of measles and epidemic levels of whooping cough.

So don't be immune to good advice: better a sore bottom, than a deadly bottom line.