Source. Dr. Mercola about an interview with Barbara Loe Fisher (my emphasis)
What You Need to Know about "Herd Immunity"
Typically, vaccine promoters will stress the importance of compliance with the vaccine schedule that requires multiple doses of a vaccine in order to create and maintain vaccine induced "herd immunity," because a vaccine is never 100 percent effective. However, they never quite seem to be able to explain why the majority of outbreaks occur in areas that are thought to HAVE herd immunity status, i.e. where the majority of people are vaccinated and "should" therefore never get the disease.
The problem is that there is in fact such a thing as natural herd immunity. But [what] they've done is they've taken this natural phenomenon and assume that vaccines will work the same way. However, they do not, and the science clearly shows that there's a big difference between naturally arising herd immunity and vaccine-induced herd immunity.
To learn more, I urge you to listen to the second video above, in which Barbara discusses the concept of herd immunity.
"The original concept of herd immunity is that when a population experiences the natural disease… natural immunity would be achieved – a robust, qualitatively superior natural herd immunity within the population, which would then protect other people from getting the disease in other age groups. It's the way infectious diseases work…" Barbara explains. "But the vaccinologists have adopted this idea of vaccine induced herd immunity.
The problem with it is that all vaccines only confer temporary protection… Pertussis vaccine is one the best examples… Pertussis vaccines have been used for about 50 to 60 years, and the organism has started to evolve to become vaccine resistant. I think this is not something that's really understood generally by the public: Vaccines do not confer the same type of immunity that natural exposure to the disease does."
Vaccine professionals would like you to believe they are the same, but they're qualitatively two entirely different types of immune responses.
"In most cases natural exposure to disease would give you a longer lasting, more robust, qualitatively superior immunity because it gives you both cell mediated immunity and humoral immunity," Barbara explains. "Humoral is the antibody production. The way you measure vaccine-induced immunity is by how high the antibody titers are. (How many antibodies you have, basically.)
But the problem is, the cell mediated immunity is very important as well. Most vaccines evade cell mediated immunity and go straight for the antibodies, which is only one part of immunity. That's been the big problem with the production of vaccines."
Definition (source, my emphasis):
The human immune system is divided into two main parts:
humoral immunity, which deals with infectious agents in the blood and body tissues, and
cell-mediated immunity, which deals with body cells that have been infected.
In general, the humoral system is managed by B-cells (with help from T-cells), and the cell-mediated system is managed by T-cells. Both systems exhibit fascinating complexity and interrelationships that allow them to fine-tune immune reactions to almost any antigen, or molecule that stimulates an immune response.
Case in point -
To Stem Mumps Outbreak, Doctors Recommend a Third Vaccination Despite Ineffectiveness of MMR Vaccine and Lawsuit Claiming Fraud (Mercola, 2006, 2009, 2010 — children, 89 to 97% properly vaccinated, still got the diseases.)