by Marco Cáceres 
Because of the recent outbreaks of measles in the United States and the re-energized public debate about vaccines and vaccination policy, we’re again starting to hear references to the theory of “herd immunity.” The theory is the foundation for the mass vaccination campaigns around the world. It currently stipulates that in order to provide immunity to a population against contagious diseases like measles you must vaccinate at least 95% of the population. Theoretically-speaking, with a vaccination rate of 95%, the diseases should be eradicated.
In an epidemiological review paper titled “Herd Immunity: History, Theory, Practice,” written by Paul E. M. Fine and published in 1993, the author notes that the first “published use” of the term herd immunity “appears to have been” in a paper titled “The spread of bacterial infection: the problem of herd immunity,” written by W. W. C. Topley and G. S. Wilson and published in 1923. From Fine’s paper, it seems that the theory of herd immunity was originally developed based on some observations with mice and some “simple mathematical formulations,” but the paper is unclear about whether the theory was ever validated through some of sort scientific peer review process…
