The Purpose of a Vaccine

Context: With three vaccines in the final stages of approval, it is crucial to define the outcomes we are expecting from population-level vaccination plans for COVID-19.

Analysis of vaccination strategy:

• Purpose of vaccination:

1. Individual protection: Ability to develop immunity by producing antibodies among those individuals who have taken a vaccine shot.
2. Achieve Herd immunity: By ensuring a threshold coverage (about 60% of the population) - the proportion of the population that needs to be covered so that the entire population is protected.

• Concerns regarding vaccination:

1. At the individual level:

• Vaccine efficacy: (a probability of preventing the infection) is limited by probable adverse side-effects of vaccination and the ability of the health system to deal with them.
• Affordability: With the absence of government intervention, vaccines would be selectively available.

2. At population- level:

• Deciding threshold coverage: at different stages of a pandemic.
• Accessibility: is limited by socio-economic (poor vs rich), ethical (elder or younger) and systemic (the ability of the health system to withstand after-effects) considerations.
• Duration of protection: provided by COVID-19 vaccine.
• Defining objectives of population-based COVID-19 vaccination drive:

1. Prioritising Health workers and then elderly population- Will protect the health system, but maybe ineffective as patients, and their caregiver consists the largest and most vulnerable.
2. Population-level immunity: Will help in the elimination of the pandemic.

• e.g. New Zealand is preparing for a countrywide immunisation programme with a goal of covering the whole population with a threshold coverage.

Conclusion: 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.