ISSN (Print) - 0012-9976 | ISSN (Online) - 2349-8846

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The Vaccine Conundrum

Vaccination is treated as a public health intervention for its ability to develop herd immunity. The newer vaccinations are transforming the very nature of intervention from a “preventive” to a “promotive” one, and from disease-specific to strain-specific one, at a time when population prevalence of the parent diseases is uncertain.

Vaccination as a public health intervention has transformed since its first successful intervention to prevent smallpox. As per the biomedical logic, the primary purpose of a vaccine is to induce immunity among individuals to prevent from those diseases against which they get vaccinated. On the other hand, there is a public health dimension, namely immunisation, characterised by its capacity to develop herd immunity, acquired by populations by achieving “threshold coverage.”1 It is this ability to develop herd immunity that qualifies vaccination as a public health intervention (Fine 1993; Patil 2011). One of the important characteristics that could prove the historic success of vaccines is the fact that most of the vaccines targeted a single disease that was prevalent at that time in epidemic proportions. Globally, World Health Organization initiated the expanded programme of immunisation (EPI) targeting those specific diseases which were highly prevalent then, namely tuberculosis (TB), diptheria, pertussis, tetanus, measles and polio. It later became part of the universal immunisation programme (UIP) in several countries, including India. Referring to the six diseases covered under EPI as “killer diseases” itself indicates the high prevalence and case fatality of those diseases (Bland and Clements 1998). From a public health perspective, herd immunity is expected to reduce susceptibility to diseases during epidemic times, as susceptibility will be higher in an unvaccinated population.

Herd immunity cannot be a population characteristic acquired extravagantly during the absence of an epidemic. Acquiring herd immunity through immunisation at a time when the population prevalence of the disease is low (Bruni et al 2018) as in the case of human papillomavirus (HPV) vaccine and the rise in vaccine virus-induced polio due to long-term use of oral polio (Sathyamala et al 2005) in the Indian context, are situations that resulted in several controversies on the vaccine policies of the government. The changing nature and characteristics of vaccines have serious implications in the current context when newer vaccines2 are included under the UIP: first and foremost, vaccines have transformed from a “preventive” intervention to that of a “promotive” intervention. Second, vaccines are no longer targeted to prevent single diseases but only a subset of those diseases caused by any specific infectious agent. The third and more disturbing aspect is that the population prevalence of those diseases for which newer vaccines exist, are either low or lack sufficient data, due to which the need for immunisation as a public health intervention for those diseases is not warranted.

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Updated On : 8th Feb, 2019

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