For those who are not aware of the term, the expression herd immunity is a somewhat slippery term (more on that below) that is viewed as an article of faith by those who are in favor of increasingly more vaccinations of children.  The basic idea of herd immunity is that by vaccinating enough people, the rest of the people in a given society will benefit from that widespread vaccination and thus certain diseases will become less prevalent.  This is the idea, at least, and it is something that is expressed often in one way or another when one is reading websites from organizations and people who support vaccinations.  When I said that herd immunity was an article of faith, though, it deserves to be mentioned that there is a remarkable scarcity of evidence to suggest that herd immunity actually works on an empirical level.  There are some reasons for this, and I would like to comment on several of them here.

The first reason that herd immunity is problematic to demonstrate is demonstrated by the abstract to a peer-reviewed paper on the subject:  “The term herd immunity has been used by various authors to conform to different definitions. Earlier this situation had been identified but not corrected. We propose that it should have precise meaning for which purpose a new definition is offered: “the proportion of subjects with immunity in a given population”. This definition dissociates herd immunity from the indirect protection observed in the unimmunised segment of a population in which a large proportion is immunised, for which the term ‘herd effect’ is proposed. It is defined as: “the reduction of infection or disease in the unimmunised segment as a result of immunising a proportion of the population”. Herd immunity can be measured by testing a sample of the population for the presence of the chosen immune parameter. Herd effect can be measured by quantifying the decline in incidence in the unimmunised segment of a population in which an immunisation programme is instituted. Herd immunity applies to immunisation or infection, human to human transmitted or otherwise. On the other hand, herd effect applies to immunisation or other health interventions which reduce the probability of transmission, confined to infections transmitted human to human, directly or via vector. The induced herd immunity of a given vaccine exhibits geographic variation as it depends upon coverage and efficacy of the vaccine, both of which can vary geographically. Herd effect is determined by herd immunity as well as the force of transmission of the corresponding infection. Clear understanding of these phenomena and their relationships will help improve the design of effective and efficient immunisation programmes aimed at control, elimination or eradication of vaccine preventable infectious diseases [1].”  Given the fact that the ambiguity of definitions of herd immunity has prevented solid empirical research from happening so far on the phenomenon, it is remarkable how it is trotted out as gospel truth when it has not even been able to be tested because of the slipperiness of how it has been defined in multiple ways.

What is interesting to note is that the authors of this paper define herd immunity as the benefit of vaccination to those who are not themselves vaccinated.  Theoretically speaking, those who choose not to be vaccinated for various grounds–and reasonable grounds for not wanting to be vaccinated certainly exist–ought not to threaten the herd immunity if the vaccines are themselves sufficiently effective.  Moreover, if vaccines are effective, the choice of people not to be vaccinated themselves or to avoid vaccinating their children should only affect those people who are not vaccinated and not those who have been, assuming those vaccines work as promised.  Bur research suggests that  several vaccines do not really work all that long at all, with flu vaccines typically failing within 90 to 180 days even when the right flu virus has been chosen, pertussis vaccines lasting only about a year or so, and the mumps part of the MMR vaccine lasting a decade or less even with those who have received a second shot of that vaccine.  That does not even take into account those vaccines whose length of effectiveness is not yet known because the vaccines have not been around long enough to know.  When vaccines do not last as long as they are supposed to, it is not merely that herd immunity is being tested, but that one is dealing with vaccines that are simply not very effective–even if one does not take into account the possibility of side effects to the daunting vaccine regimen that schools demand for contemporary children.

What do all of these problems have to do with each other?  For one, they suggest that even on scientific levels, from sources that are by no means hostile to vaccination, there are serious problems with the idea of herd immunity, not least because the term is so ambiguously defined that it is has been difficult to test the concept empirically and because some vaccines simply do not work very well and thus provide little protection over time to those who get the vaccines and can thus not provide any herd immunity for those who are not vaccinated.  It should be noted as well that none of these problems are the fault of those who oppose vaccinations, and that these problems with the idea of herd immunity exist apart from any concerns about side effects or the materials and procedures that went into making vaccines, which are both problematic enough.  Before those who support vaccines vent their spleen against those who oppose vaccines and try to hype the idea of herd immunity, perhaps it would be good to make sure that vaccines were good enough to protect those who got them first, so that they can start protecting those who, for whatever reason, do not wish vaccination for themselves or their children.

[1] https://www.ncbi.nlm.nih.gov/pubmed/11078115.  Accessed 7 July 2019 by the author.