Planning for a national Covid-19 vaccination programme has begun to move forward in right earnest in India. Last week Union Health Secretary Rajesh Bhushan wrote to state governments outlining the administrative structures to be put in place to oversee the implementation in their respective jurisdictions. As of now, the Narendra Modi government expects the vaccination programme to take over a year, with healthcare and essential services workers getting the shots before the rest of the population. The Modi government has done well to reject the narrative of low expectations by setting a one-year timeline. As I have argued earlier, this is both necessary and eminently doable if we do not limit ourselves to departmental thinking and processes.
As a multidisciplinary team of my Takshashila colleagues has proposed, India should aim to vaccinate 80 per cent of the population by 31 December 2021 at a cost of Rs 50,000-250,000 crore depending on the type of vaccine. India can not only afford such a programme, it can’t afford not to.
Conversations over our vaccination policy proposals revealed a genuine debate over the number of people who need to be vaccinated. Should it be as high as 80 per cent, as we have proposed? Or is 80 per cent too low? Much of the debate on how many people need to be vaccinated comes from epidemiology — specifically from the notion of “herd immunity”, or more properly “herd protection”. As Christie Aschwanden writes in the excellent article in Nature, “Herd immunity happens when a virus can’t spread because it keeps encountering people who are protected against infection. Once a sufficient proportion of the population is no longer susceptible, any new outbreak peters out.”
India’s herd immunity status
Now, herd immunity can happen either when enough people develop natural immunity (after contracting the disease and developing antibodies for it) or when they have been vaccinated.
Using the basic reproduction number R0 (the number of people a single infected person would infect in a susceptible population), for SARS-CoV-19, the herd immunity threshold is between 50 per cent and 67 per cent of the population. On a nationwide level, this means that 65-87 crore people must acquire immunity. However, as epidemiologist T. Jacob John told Science magazine’s Vaishnavi Chandrashekar, a big national epidemic is a “figment of statistical imagination” and it is more correct to see over a 100 smaller epidemics occurring across the country. In other words, 50-67 per cent of various state and local populations must have immunity before their epidemics come to an end.
In the West, there is a political-ideological debate that uses the herd immunity threshold to argue for exposing healthy people to the virus while protecting the vulnerable segments like the elderly and those with co-morbidities. Fortunately, this scientifically questionable, highly risky, practically challenging, ethically problematic and politically charged approach does not find much favour in India as an intentional policy approach. Yet, given the highly variable adoption of masks, hand washing and social distancing, as well as the limitations of the public health machinery across the country, part of the way India is actually coping with the pandemic involves unintentional exposure to infection. As my COBOTE (Cynically Optimistic Back of the Envelope) estimate and the government’s delightfully named Covid-19 India National Supermodel Committee reveal, the real extent of the pandemic in India is likely much higher than what the official numbers show, meaning that crores of people in the country already have antibodies.
Why 80 per cent
Does this mean that the national vaccination targets can be lower because India only needs to vaccinate those who do not have antibodies? Not quite. First, going by the experience of the ordinary flu viruses, post-infection immunity is not permanent, and lasts for a few months to a few years. Second, the cost of testing for antibodies is similar to the cost of vaccination. Therefore, it is necessary to immunise people regardless of whether they have previously suffered Covid-19 infection. This is true even if the vaccine itself offers only temporary protection, and must be taken on an annual basis.
A number of people have wondered why, given that epidemiological calculations indicate a herd immunity threshold of 67 per cent, should we target 80 per cent of the population for vaccination? The answer is that the public policy target is different from the purely epidemiological target for a number of reasons, the first of which is uncertainty. Given that we are not sure at this time if even 67 per cent is enough, it is better to have a safety margin to ensure that the vaccination programme is successful. Second, the fixed costs to immunise 67 per cent and 80 per cent are more or less the same, but the incremental benefits of vaccinating a higher number are higher than the incremental costs. Finally, designing the system to have the capacity to handle 80 per cent of the population allows us to relatively easily extend it to 90 per cent or higher should that become necessary.
As Jacob John’s words remind us, when we say India must vaccinate 80 per cent of its population by the end of 2021, what it should correctly mean is that states, municipalities and district administrations should cover 80 per cent or more of their populations. That is what every administration in India should be planning at this time.
Nitin Pai is the director of the Takshashila Institution, an independent centre for research and education in public policy. Views are personal.