Herd immunity is an epidemiologic construct

“Herd immunity is not an immunologic idea, but rather an epidemiologic construct, which theoretically predicts successful disease control when a certain pre-calculated percentage of people in the population are immune from disease. A scholarly article on herd immunity states:

Along with the growth of interest in herd immunity, there has been a proliferation of views of what it means or even of whether it exists at all. Several authors have written of data on measles, which “challenge” the principle of herd immunity and others cite widely divergent estimates (from 70 to 95 percent) of the magnitude of the herd immunity threshold required for measles eradication.

Herd immunity has been deemed instrumental in rapid disease eradication.  Relying upon the meticulous work of Dr. A. W. Hedrich, who documented annual measles attack rates in relation to the proportion of naturally immune people in the 1900s-1930s, the United States Public Health Service had confidently announced in 1967 its intent to swiftly eradicate measles in the USA over the Winter by vaccinating a sufficient number of still susceptible children. Mass vaccination was implemented, but the expected herd-immunity effect did not materialize and measles epidemics did not stop in 1967.”

— Tetyana Obukhanych, PhD, immunologist

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2 thoughts on “Herd immunity is an epidemiologic construct

  1. I would expect a little more depth from her but then again she has chosen her agenda. There was a herd immunity effect that helped reduce dramatically epidemics, but it cannot be expected to prevent outbreaks especially given the unprecedented mobility and density of the population and the changing vaccination rates. It is a straw man argument to say that herd immunity is ineffective in light of outbreaks or even the occasional epidemic, which virtually always occurs because of low vaccination rates. It is also a bit absurd to assume that in the very beginning of the measles vaccine policy implementation that those developing it would get it right the first time, or the second. Here is an interesting study of a real California measles epidemic that occurred clearly because of low vaccination rates. Epidemics have occurred not despite herd immunity but because, in certain areas, it did not exist. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1022280/?page=1

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    1. “Epidemics have occurred not despite herd immunity but because, in certain areas, it did not exist.” Better said, epidemics like the one in California many years ago have occurred not because there is no such thing as a herd immunity effect within the context of vaccinations (say for measles) but because in some areas the vaccination rates were too low. And again, herd immunity does not mean “no outbreaks.”

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