Smallpox is the perfect example of what we hope to achieve with immunizations. With the proper and complete implementation of smallpox vaccines, the disease was completely eliminated and we no longer need to be immunized against it! Smallpox was no minor illness, either. Just in the 20th century, it was responsible for 300-500 million deaths, as well as millions and millions more throughout history. Now think about that number, and now think how we no longer need to worry about this terrible disease. Thanks to vaccinations, we don't really have to worry about a number of diseases today.
Below are some other examples of how well vaccines are doing their job in reducing infections.
Meningitis (Haemophilus influenzae)
There used to be about 20,000 cases of Haemophilus influenzae (type b) in children and infants each year, but after the introduction of the Hib vaccine in 1987, the incidence of this infection decreased by 98%.
Polio
Through the 1940's and 50's, there was an average of around 16,000 paralytic cases of polio each year just in the United States. Paralysis was only seen in about 1% of cases, though, with more people being asymptomatic or experiencing mild symptoms. Still, the virus spread so easily that thousands were severely affected each year. Just ten years after the introduction of the Salk vaccine in the United States, only 61 cases had been reported. Although the United States experienced a lot of success from the vaccine, the rest of the world was still experiencing the polio endemic through the 80's, until the World Health Organization decided to try and eradicate the disease in 1988. Since then, the worldwide totals have declined from 350,000 cases to just 187 in 2012, nearing ever so closely to the goal of eradication.
Here is a nice graph of the cases of polio in the United States.
Diphtheria
There were about 200,000 cases of diphtheria each year in the U.S. before a vaccine was developed. Now, there have only been 5 total cases in the past 10 years!
Mumps
Mumps is a (usually) mild virus that is covered by our MMR (Measles, Mumps and Rubella) vaccine. It is a major cause of deafness in children though, and can also cause orchitis (swelling of the testes) in males. Before a vaccine was developed, we saw about 300,000 cases each year, reduced to under 300 cases in 2001.
Hepatitis B
The Hepatitis B Virus has infected 2 billion people in the world at some point. 2 billion! This is a virus that is associated with liver problems, and about 25% of people who catch it would be expected to die as a result of it sometime in their lives. In the 80's, more than 450,000 people were infected with the virus each year. Now, this number has been reduced to less than 80,000 each year thanks to vaccination.
Rubella
Rubella, another virus covered by the MMR vaccine, is heavily associated with causing miscarriages and birth defects in pregnant women who acquire the illness. In 1964, before routine use of a vaccine against Rubella, there were 11,000 miscarriages and 20,000 infants born with defects as a result of the virus. By 2,000, there were only 6 reported cases.
These are only a few of the illnesses covered by vaccines today. To learn about more, I'd suggest visiting CDC-Vaccine-Preventable Diseases
Well since we barely see these things anymore, can't we just stop vaccinating?
Well, no. Luckily there were other places "courageous" enough to have this same line of thinking to make answering this easier. Sure we're seeing fewer and fewer cases through the years, but this doesn't mean the pathogenic agent has just disappeared, and it certainly doesn't mean it can't easily be brought over from another country. Take, for example, the Soviet Union. Before its collapse, it had similar vaccination programs to ours, and as a result, the diseases vaccinated against were uncommon. But, when the USSR collapsed, several things went with it, including their record keeping and the standards of their immunization program. Shortly after, the area experienced an epidemic of diphtheria, with about 200,000 cases being reported.
Japan also provided a wonderful example of why you can't just stop vaccinating until a pathogen is completely eradicated. In the 70's, rumors spread about the pertussis vaccine's efficacy and safety, so people stopped getting them. In just a few years, the incidence of pertussis in Japan increased by 3,200%! And, of course, shortly after, Japan's government learned from their mistake and began mandating the vaccine.
I know people who don't get vaccinated, and they've never caught any of these things.
Of course not everyone is going to catch these illnesses, that would still be the case even if nobody got vaccinated. The fact is that people who are immunized are less likely to become sick, and in the event that they still do, they most often suffer very mild symptoms compared to their unvaccinated counterparts. People who do not get vaccinated fortunately still benefit from everyone else that does, a concept known as herd immunity. In herd immunity, the large majority of a population is immune to a pathogen, thus, it is much harder for said pathogen to transmit person to person and infect those who aren't immune. If everyone stopped getting immunizations, herd immunity would soon become irrelevant. Wiki has a nice table demonstrating how many people need to be immunized for herd immunity to be effective.
Conclusion: vaccination is important!
