The science of “herd immunity” should be explained to the parents in terms they can easily understand. In general, herd immunity occurs when a sufficient rate of immunity, through vaccinations, is achieved within the community to greatly reduce the risk of infection in not only those immunized but especially in those persons who have not been immunized. Each infectious disease entity has its own threshold of immunization rate for producing herd immunity, based in part on its basic reproduction factor (contagiousness).
An informative exercise for the otolaryngologist, as well as the parents, is to access the NIH Disease Transmission Simulation site, which, given a certain infectious disease, can show how the rate of infection can vary with the percent of community immunization (available at science.education.nih.gov. If one were to use the following data in the simulator for a measles outbreak in a community—0.1 virulence rate (likelihood of dying from the infection), 10-day duration of infection, 9.0 rate of transmission—and observe the resultant spread of disease through the community population comparing 70%, 80%, and 90% initial immunity rate, it is obvious that 90% herd immunity would be required to reduce the spread of disease below the level of an “epidemic.” This is very convincing, graphic evidence.
Vaccine hesitancy is very complex and is dependent upon the context of the particular family perspective and health status. Primary factors in hesitancy are misunderstanding and misinterpretation of the science of vaccines, as well as misconceptions furthered by social media and unsubstantiated “reports.” For example, it is agreed in the legitimate scientific community that rigorous meta-analyses of available data do not support vaccinations as a cause of autism—yet parental concerns persist. It is true that vaccines are not without risks; however, the risks are very rare, and vaccines are heavily regulated by the appropriate federal agencies to comply with high safety standards. Substantial risks are quickly investigated, and action is taken to identify the potential problem, and is followed by appropriate remediation.