What is Herd Immunity?
In 1933 Dr AW Hedrich put forward a theory based on his observations of the community that he had lived in for the previous 30 years. He noted that if 68% of the community caught measles by natural infection, the other 32% of the community appeared to be protected and did not catch the measles. This theory was called “Herd Immunity” and that is all it is, a theory. It was made before there were any vaccines for measles, based on the population catching the wild measles virus, not on a population being injected with the measles vaccine virus and it has never been proven since in either an unvaccinated or vaccinated population.
The World Health Organisation (WHO) also states, “Herd immunity theory proposes that, in diseases passed from individual to individual, it is difficult to maintain a chain of infection when large numbers of the population are immune.” Please note that the WHO says “theory” and “proposes”, so it is not a fact, it is only a speculation or hunch (definition of theory) that has been put forward for discussion and consideration (definition of propose). Also observe that the WHO are saying this applies when a disease is passed from one individual to another as in one person catching the disease and infecting another, nothing about vaccinations. In fact there are studies showing that even when regions have a 99% uptake of the measles vaccine, measles as a disease still exists. So this would suggest that vaccines do not confer herd immunity at all.
It is known that measles, mumps, rubella and varicella zoster virus (VZV/chickenpox) infections are regarded as typical diseases of childhood and that they are normally clinically mild and result in lifelong immunity (link). It is also known that the immunity conferred by vaccines is of short and unknown duration. So this is creating a problem because the more children that do not catch these diseases in childhood the more adults who are likely to catch them later on in life when any immunity they may have had wears off; and while these diseases are mild in children they are not in adults. Indeed mumps in adult males can cause sterility.
Hedrich, A. W. “MONTHLY ESTIMATES OF THE CHILD POPULATION ‘SUSCEPTIBLE’ TO MEASLES, 1900-1931, BALTIMORE, MD.” American Journal of Epidemiology 17.3 (1933): 613-636.
Global Manual on Surveillance of Adverse Events Following Immunizations. World Health Organization, 2014. Print.
Epidemiological analysis of immunity against vaccine-preventable diseases: rubella, measles, mumps and chickenpox. National Center for Biotechnology Information/National Library of Medicine / National Institutes of Health.