The purpose of a vaccine

It is crucial to define the outcomes we are expecting from population-level vaccination plans for COVID-19

Published - December 03, 2020 01:15 am IST

A woman holds a small bottle labelled with coronavirus vaccine sticker in this illustration picture. File

A woman holds a small bottle labelled with coronavirus vaccine sticker in this illustration picture. File

While the whole world waits for a COVID-19 vaccine as the last resort to control the pandemic , it is important to examine the challenges it poses to qualify as a ‘public health’ intervention in India.

Vaccinations have a dual purpose. First is the ability to develop immunity by producing antibodies among those individuals who have taken a vaccine shot. In the midst of a pandemic, the popular perception for vaccination is that which safeguards oneself from the disease. It is this individualistic need that generates a huge demand for vaccines in the market, which, in the absence of government intervention, will be affordable only for those who can pay for them.

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The second and more crucial purpose of vaccination is to achieve herd immunity in a population by ensuring a threshold coverage — the proportion of population that needs to be covered so that the entire population is protected. The threshold coverage for any disease in a given population is based on the vaccine efficacy in a population, the rate of spread of infection through it, also known as infectivity rate, and the natural immunity that already exists in the population due to prior exposure to the same disease or through cross infections. The threshold coverage is estimated to be around 60% for COVID-19 vaccine to achieve population-level immunity, which should ideally vary, depending on different stages of the pandemic.

While deciding on whether vaccines need to be introduced amid a pandemic, there can be individual as well as population-level considerations. The concerns raised in the context of individual prevention include vaccine efficacy, which is generally defined as the probability that an individual, if vaccinated, can prevent the onset of infection. Equally important is the probability of adverse reactions that can arise among individuals. Both these parameters must be considered even to qualify vaccines as potential candidates for a public health intervention.

However, there are several other complex economic, social, ethical and systemic factors that need to be looked into. Already, there are concerns raised about the economic resources needed to make the vaccine available for a large population: will it be provided free at the point of delivery or will it be charged? How will an already weakened health system be able to take on the vaccination drive that is expected to cover the entire population? What is the cost of ensuring necessary support services, including cold chains and human resources required for effective vaccine delivery? The most difficult ethical question posed is about who should be prioritised and what the basis is for such prioritisation. Equally relevant is the projected proportion of the population that may face adverse reactions and the ability of the health system to respond to those. Another aspect specific to the COVID-19 vaccine is the duration of protection provided.


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Unclear objectives

These are all important questions, but they will arise only when the most important public health purpose of vaccination — as an immunisation programme — is convincingly answered. In the Indian context, it is not clear what outcome is expected of a population-based vaccination programme for COVID-19. The most dominant argument is that health workers need to be covered on a priority basis, and then the elderly. One of the arguments posed for targeting health workers is that it will protect the health system from collapsing due to COVID-19. If this is so, how can we think of the health system as comprising only health workers, when a majority of stakeholders, even in terms of mere numbers, are always the patients and their caregivers. Second — and more crucial — is the goal of population-level immunity, which is the expected outcome of any population-level vaccination drive. Its very purpose will be defeated if only a specific population group is targeted, when the pandemic can infect all groups similarly. In New Zealand, preparations are on for a countrywide immunisation programme with a goal of covering the whole population with a threshold coverage.

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Like other public health programmes, it is safe to demonstrate the success of vaccination as a public health intervention in a small population, like a block or a district, before scaling it up for the national level. If population-level immunity is not the focus, then the key purpose of COVID-19 vaccines will be to ensure individual immunity, which might operate within the logic of the market. We should not forget that it took us more than 13 years to declare eradication and achieve population-level immunity for a disease like polio, which targeted only children.

Mathew George is Professor at the Centre for Public Health, School of Health Systems Studies, Tata Institute of Social Sciences, Mumbai

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