How much does vaccine refusal reduce the effectiveness of vaccinations in the community, and how much does this have the potential to harm even people who get vaccinated?
Davis: To understand the impact of vaccine refusal, we need to remind ourselves how vaccines help prevent disease.
Vaccination protects against illnesses in two main ways. First, the person being vaccinated is protected, because the vaccine stimulates his or her immune system to recognize the harmful bacteria or virus in the future and provide a protective response. This is the process of being “immunized.” Vaccines are developed to provide the benefits of immunization as effectively as possible to all people who receive them, while producing as few side effects as possible. However, just as people vary in the benefits they get from prescription medicines, people also are different in their immunity from vaccination. Many people get maximum benefit while some not as much. In addition, protection from vaccination can decrease over time. Doctors call this “waning immunity.”
That’s what makes herd immunity — the second form of protection from vaccines — so important. Just as a herd of animals will form a protective circle around its most vulnerable members, herd immunity refers to how well immunized people in a community protect the less- or nonimmunized people in that same community. This is an extremely important benefit of vaccination programs, because not everyone can receive vaccines, for medical reasons, and because some people who have been vaccinated will not fully respond. When it comes to battling diseases, humans need the protection of herds, too.