Month: June 2015

The Power of Herd Immunity

The state of California is currently debating legislation that will require all children to be vaccinated. Senate bill 277 will ensure that 10 childhood diseases will be prevented as the law will direct that vaccines for these diseases must be administered prior to admission to kindergarten or any daycare setting. Under this proposed law, only medical exemptions will be allowed to circumvent mandatory vaccination.

Vaccine exemptions exist in many forms and vary from state to state as to which are legal and how they are granted. One major type is that of a personal exemption. These exemptions are based on the belief that vaccines do more harm that good or that calling for mandatory vaccination is an infringement on personal liberty, that no government entity has the right to mandate vaccination. Personal exemptions however greatly undermine the power of medical exemptions which are important for those who cannot be vaccinated due to documented medical conditions. Religious exemptions are granted when vaccination policies are at odds with a person’s religious beliefs. Of the exemptions I have just briefly described, religious and medical exemptions appear to be the most reasonable to grant as the practice of one’s religion is a right granted by the constitution while medical as I mentioned is stating that the vaccine could be harmful to an individual’s health due to a preexisting medical condition.

No matter which of the three exemptions are granted, vaccination is still very important. Establishment of herd immunity and maintaining a high percentage of vaccinated individuals within a population reduces the incidence of disease within a population. How? I will use a very simplistic example with ten people (we know that this is an inappropriate sample size, but this is to illustrate the point).

Scenario 1: Of the ten people in this population, only 1 is vaccinated (10% vaccination rate), 1 person is infected (10% infection rate) and the remaining eight people are not vaccinated. Thus, we have 80% of this example population that is susceptible to disease and with a low vaccination rate, infection is rapid among the non-vaccinated.

Scenario 2: Vaccination rate increases to 50% (5 vaccinated individuals), only one infected individual and four non-vaccinated. Here, susceptibility has been halved from scenario 1 (40%) but it is still not enough to keep infection from passing readily through this population.

Maximum protection of the population (vaccinated as well as the non-vaccinated), we need the vaccination rate to be at 90% or higher and only 10% of the population is susceptible to infection. Looking at that, 10% may still be too high of a susceptibility rate but what this number really means is that the chances of infection are greatly lowered and can really be better defined as sporadic. This is due to the high percentage of the population that acts essentially to buffer the effects of the infection among the population.

In a perfect world, 100% of the population would be vaccinated, thus no one would suffer from disease. A rate of 90% is acceptable, although with the current state of vaccination in the U.S., this number has dwindled, placing us in a very dire state. If not for yourself. vaccinate for the good of all. Our fortunes against infectious disease rise and fall with every action we take or every opportunity we squander.