When the number of unvaccinated people in a community increases, so does the risk that a serious vaccine-preventable illness can take hold and cause an outbreak. As more people vaccinate, a disease’s chance of causing damage to a community is greatly reduced. This is known as “herd immunity” or “community immunity.” Think of camping as an analogy. If everyone at a campground properly stores their food, bears won’t be enticed to come around. If even one person leaves their food unprotected, it invites bears in to investigate all the campsites for opportunities to eat.
In the U.S., vaccines have reduced or eliminated many infectious diseases that once routinely killed or harmed many infants, children, and adults. However, the viruses and bacteria that cause vaccine-preventable disease and death still exist and can be passed on to people who are not protected by vaccines. Vaccine-preventable diseases have many social and economic costs: sick children miss school and can cause parents to lose time from work. These diseases also result in doctor’s visits, hospitalizations, and even premature deaths.
When a critical portion of a community is immunized against a contagious disease, most members of the community are protected from that disease because there is little opportunity for an outbreak. Even those who are not eligible for certain vaccines—such as infants, pregnant women, or immunocompromised individuals—get some protection because the spread of contagious disease is contained. This is known as “community immunity.”
For example, in 1974, Japan had a successful pertussis (whooping cough) vaccination program, with nearly 80% of Japanese children vaccinated. That year only 393 cases of pertussis were reported in the entire country, and there were no deaths from pertussis. But then rumors began to spread that pertussis vaccination was no longer needed and that the vaccine was not safe, and by 1976 only 10% of 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.
If people in the United States stopped vaccinating, especially in large numbers, diseases that are almost unknown would stage a comeback. Before long we would see epidemics of diseases that are nearly under control today. More children would get sick and more would die.
We don’t vaccinate just to protect our children. We also vaccinate to protect our grandchildren and their grandchildren. With one disease, smallpox, we eradicated the disease. Our children don’t have to get smallpox shots anymore because the disease no longer exists. If we keep vaccinating now, parents in the future may be able to trust that diseases like polio and meningitis won’t infect, cripple, or kill children. Vaccinations are one of the best ways to put an end to the serious effects of certain diseases.