Excerpted from Immunization: History, Ethics, Law and Health By Catherine Diodati
Utilitarianism and herd immunity are central correlative concepts in this discussion on mass immunization. Utilitarianism refers to the belief that the greater value (utility/usefulness) of a certain act or rule must be that which secures the greatest benefit for the greatest number. Herd Immunity refers to the level of disease resistance of a community or population. Herd immunity is associated with mass immunization by virtue of the belief that if high percentages of a population or community are adequately immunized against certain diseases, virtually all persons will be protected from disease.
Immunization against rubella presents an interesting example of both the utilitarian rationale behind mass immunization and of the sometimes perverse effects of inadequate immunity thresholds and of achieving targeted immunity thresholds but within the wrong herd population. Mass rubella immunization, perhaps one of the clearest examples of immunization for utilitarian purposes, is meant to offer protection, not to the vaccine recipient but, to fetuses in utero whose susceptible mothers may contact an infectious carrier. Although contact with the rubella virus does not always result in congenital rubella syndrome (CRS), the fetus of a non-immune mother who comes into contact with the virus during the first trimester of pregnancy may be at risk. For all other populations, “rubella is a benign disease that does not justify prevention by vaccination.”
To determine the herd immunity threshold for rubella immunization, health care professionals needed to consider whether it was more effective to inoculate young children (reducing the risk of infection) or whether to concentrate inoculations on adolescent girls prior to child bearing age (decreasing the number of susceptibles).
It appears to be the current practice in Canada, the United States, and the United Kingdom to immunize children soon after their first birthday thus reducing the circulation of the wild virus among children. This method for creating herd immunity has been described in the following way:
Mass childhood rubella immunization programs designed to produce “herd immunity” are intended to prevent the spread of rubella to one “herd”, susceptible women of childbearing age, by creating a high level of immunity in another “herd” – young population groups. Vaccinating children en mass against rubella is not justified by any significant health benefits accrued by the children themselves. Instead, inflicting some measure of pain and risk of adverse events (e.g. arthritis, autism, etc.) on this one target population has been justified by the greater utilitarian good proposed for another population.
It was determined that an 80-85% rubella vaccine threshold coverage is called for in order to induce herd immunity. Theoretically, unless the number of immunes reach the targeted goal, either by contracting the disease naturally or by vaccination, a “proportion of women of reproductive age [remain] susceptible to the virus and the number of cases of congenital rubella syndrome actually increase[s].” While this may be true for inadequate immunity rates, it appears that adequate vaccine-induced herd immunity rates may result in the same perverse consequences.
In the United States, the number of CRS cases reported for 1969, the year the rubella vaccine was licensed, was 31; that number represents a nearly three-fold increase in cases reported for each of the three preceding years. Certainly, as the above theory suggests, the initiation of rubella immunization, which would not reach herd immunity rates within the first year, could have resulted in an increase in CRS. Oddly enough, and perhaps unpredictably, the number of CRS cases did not decline in the following years despite widespread vaccination. In 1970 and 1971, CRS cases soared to 77 and 68 respectively. In fact, the number of CRS cases remained at very high levels (30-62 per year) for over a decade before they returned to the pre-vaccine rates. Quite simply, this method of protecting one “herd” by creating immunity in another “herd” failed dismally.
Initially, the vaccine had “little or no impact on the number of [rubella] cases reported” but, even when incidence rates fell into decline during the 1970’s there was no concurrent progressive decline in CRS until the early 1980’s. What actually happened is that rubella infections became less common in young children but appeared more frequently in older adolescents and adults which posed a greater health risk for women of reproductive age. In 1980 Dr. Cherry, a member of the Advisory Committee on Immunization Practices, explained that “essentially we have controlled the disease in persons 14 years or younger but have given it a free hand in those 15 or older.” Contrast this with the fact that naturally occurring rubella epidemics, in the pre-vaccine era, “produced immunity in about 80% of the population by 20 years of age” and it becomes evident that, by targeting the wrong “herd”, this immunization strategy produced the opposite results of those anticipated. Furthermore, from 1970-1988, Britain adopted the strategy of immunizing only adolescent girls and susceptible women and, while this strategy did not decrease the number of rubella cases, CRS cases decreased, albeit slightly. Similarly, from 1979-1982, the US adopted this same strategy and by 1981 there was a significant decline in CRS cases.
Even though the US returned to the childhood vaccination strategy, both rubella and CRS cases continued to decline, except for occasional divergences. It has been suggested, however, that the more recent decline in CRS may be attributed to other significant “hidden” factors such as a fall in the fertility rate and the more frequent use of therapeutic abortions post-exposure. It seems fairly clear that even if herd immunity thresholds are reached, but they are not reached in the proper populations, the results are disastrous and contrary to the goals of the herd immunity theory.
If only susceptible women of childbearing age were targeted for immunization against rubella, it is unlikely that the US would have experienced such a dramatic increase in CRS cases. Furthermore, this strategy would have conformed more closely to the utilitarian ethic in a variety of ways. The vaccine-related costs, pain and adverse events would have been less burdensome overall. If the naturally acquired disease continued to produce immunity in 80% of the population, then only a small percentage would require immunization, fewer individuals would suffer discomfort, pain and adverse events from the vaccine and the associated costs. It seems fairly clear that if vaccine-derived herd immunity really is an utilitarian benefit, then the target populations must be appropriate or else the result is disastrous.