Aren't these diseases mostly gone now?

It is true that many diseases such as polio and diphtheria are less common. Why is this so? It is because they have effectively been reduced to record lows through vaccination.

When most of us get immunized, something called "herd immunity" makes it harder and harder for the disease to spread from person to person. This is especially important for people with certain medical conditions who are at a higher risk of getting a disease because they cannot be immunized.

What happens if we stop immunizing?

But, if we stop immunizing, the diseases will come back, making it especially risky for those who are at risk. In some cases, these diseases are just a plane ride away.

Let's look at what happens when immunization rates drop significantly in other countries. 

Measles in Ireland

Ireland saw measles soar from 148 cases in 1999 to 1200 cases in 2000 when MMR (measles, mumps and rubella) immunization rates dropped to 76% in response to concerns of a link between MMR and autism. Several children died in this outbreak.

Pertussis in Japan

In 1974 in Japan rumors began to spread that pertussis vaccination was no longer needed and that the vaccine was not safe. By 1976 only 1 in 10 infants were getting vaccinated. In 1979 Japan suffered a major pertussis epidemic, with more than 13,000 cases of whooping cough and 41 deaths. In 1981 the government began vaccinating with acellular pertussis vaccine, and the number of pertussis cases dropped again. When enough people stop immunizing, there is more disease and children may die.