Satyajit Rath: ‘The idea of herd immunity is not useful as a policy goal’

Interview with Satyajit Rath, immunologist and visiting faculty, Indian Institute of Science Education and Research, Pune.

Sathyajit Rath.

Satyajit Rath trained as a physician and a pathologist in Pune and Mumbai in the 1970s and 1980s. He has worked on mechanisms involved in the development and functioning of the immune system in India and overseas, then as a faculty member at the National Institute of Immunology in New Delhi and, since his retirement, in honorary capacities at the Indian Institute of Science Education and Research in Pune. Excerpts from an interview he gave Frontline .

Several countries that have achieved high vaccination rates are witnessing a large number of COVID-19 cases, reportedly among the unvaccinated. Does this mean that there is no real hope of populations achieving herd immunity even through vaccination?

The idea of herd immunity is a retrospective one, used as an explanation when a situation arises in which everyone is not vaccinated or infection-experienced for a given infectious disease, yet susceptible people are not getting infected (more correctly, sick). The idea of herd immunity is not particularly useful as a policy goal as COVID-19 policy experiments around the world over the past year and more have sadly shown. Also, we need to be clear about what exactly we are hoping to achieve this herd immunity for. If it is to reduce or halt the occurrence of illness, we may well discover, eventually, that it has happened, more or less. The current trends are, in fact, in that direction. If it is to reduce or halt the occurrence of asymptomatic infection, I do not think we have any real chance of doing that to any major extent.

It is said that vaccination reduces the chances of COVID-19 infection and tends to reduce its intensity but does not have a similar effect on reducing transmission. Is the evidence on this unambiguous and is this the reason why those who are unvaccinated remain vulnerable even if they are in the minority?

As I pointed out above, infection is not the same as illness and simply means that the virus has grown in the body. So everyone infected with the SARS-CoV-2 virus does not become ill, leave alone severely ill. Transmission is, usually, simply the spread of virus from one body to another, so infection is likely to correlate much more closely with transmission than it does with illness or disease. Vaccination protects very well against illness and disease. It also reduces the magnitude of virus growth in the body even when it does not quite prevent it completely. So it does reduce the magnitude and duration of infection and, therefore, of transmission. However, it does not do this as potently, so vaccination is not a guarantee of stopping transmission, which means that the unvaccinated do remain at risk of infection from asymptomatically infected vaccinated (and even more from other unvaccinated) people. And, of course, if they are in the high-risk categories, they then run the risk of severe illness.

Is there any evidence that antibodies acquired through vaccination and those acquired through exposure to infection respond differently in terms of development of immunity and transmission of virus, particularly in the context of emergence of new variants?

There is some emerging evidence that the exact nature of antibodies generated by vaccination versus infection are different, just as there is some evidence that the antibodies generated by different vaccines may also be somewhat different. These differences are of magnitude and duration in some instances and related to more subtle binding abilities in others. And the duration of antibodies generated by infection seems somewhat more variable than that of antibodies generated by vaccination. However, all of this is currently uncertain, with independent studies not necessarily showing the same things.

A large part of the Indian population today falls into one or more of three overlapping categories, each with large numbers: those carrying antibodies because of prior exposure to infection, those who have received a single vaccination dose and those who are fully vaccinated. Does the first category mean that the risks of new major outbreaks are low even though only less than a third of the adult population is fully vaccinated?

This is the case if we accept the data at face value and define major outbreaks as nationwide “waves”. My worry is that the sero-surveys, on which the claim that India has a very large proportion of “those carrying antibodies because of prior exposure to infection” is based, have all been relatively modest in size, and we are assuming that they do reflect reality accurately. Also, when we say that “X per cent of the population of a city falls in this category”, we tend to assume that this percentage is uniformly seen across the city, for example. Neither of these assumptions may be strong enough for us to think that the risk of a new wave is low. Added to this is the fact that the overlap, as you put it, among these three populations is likely to be very large, and a diverse set of marginalised communities may not fall into any of them. And finally, a single vaccine dose is nowhere near as good as the two-dose schedule, leaving a very large fraction of the population at reduced but still substantial risk. All of these worries are consistent with the fact that we keep seeing small, local outbreaks around the country even now.

India is still struggling to reach the target of fully vaccinating 80 per cent of its adult population by the year end. Going forward do you think that we have to be prepared for the possibility that vaccination of even children and booster doses may be necessary?

I certainly think that vaccination of children is advisable and is, in fact, overdue. I worry that we sometimes seem to think of COVID-19 vaccination as some sort of a “risky” matter and almost seem to be wanting to protect children from it rather than wanting to protect them from COVID-19. The vaccination of children will protect them from rare severe COVID-19 illness, and it will reduce the extent of virus transmission in the community. As for booster vaccine doses, I have yet to see strong evidence of major reduction in the protection against severe illness provided (even against current virus variants) by standard vaccine dose schedules, so I do not see any reason to be starting a major large-scale booster vaccination campaign as yet.

However, our knowledge is quite incomplete as yet on a number of counts. How long does the protection by current vaccines (and/or infection) last? What, if any, newer virus variants are arising even as we speak, so to say? And what might be their sensitivity to current vaccines? If they show some vaccine resistance, can that be overcome simply by additional booster doses of current vaccines, or will we need new-generation “variant” vaccines? These questions and emerging answers to them will determine policies and decisions about future vaccination/s as SARS-CoV-2 shifts from the epidemic stage to the endemic situation.

Looking at the global scenario, how significant are the implications of vaccine inequality for countries like India? Has India underperformed in leveraging its legacy of being a major vaccine manufacturer to contribute to the global vaccination effort, or has it done the best that could be expected of what is still a lower-middle-income developing country?

This is a complicated question. Firstly, my view is that India’s COVID-19 vaccination campaign has done as well as could be realistically expected of an enormous, messy, largely poor and deeply unequal country. Is it a great achievement? Clearly not; India went from 10 per cent of people fully vaccinated on August 27 to 20 per cent of people fully vaccinated on October 16.So a 10 per cent increase in full vaccination has taken a month and a half; at this pace, achieving the stated goal of full vaccination of about 65 per cent of the population in the next month and a half looks difficult. Further, there is considerable vaccine inequity: our largest rural States, Uttar Pradesh and Bihar, currently have less than half the vaccination coverage that Kerala, for example, has. There is every likelihood therefore that more examination will reveal substantial inequities along the expected lines of lack of access to and/or uptake in poor, rural, remote and otherwise marginalised communities.

Has India leveraged its legacy of being a major vaccine manufacturer? I think that it has not, and I think that the fault lies not with the private sector vaccine manufacturers but with us because we have abandoned, over many decades, our “legacy” capabilities of manufacturing vaccines as a major social good in public sector industries. The result has been that the deployment of India’s vaccine-manufacturing capacities for the pandemic has been significantly shaped by considerations of commercial competition. The Union government has played very much of an indirect role in the matter. It is, therefore, not surprising that we have had many occurrences of vaccine confusion: the Covaxin imbroglio, the COVAX supply turnarounds, the lack of early vaccine mix-and-match trials, the lack of systematic large-scale data collection regarding vaccine-mediated protection, and the like. And, finally, all of these limitations have been brought into stark relief, paradoxically, by our apparently extreme need to brag.

The government celebrated the event of touching the 100-crore vaccination mark as did a section of the media. Would you say the celebration was expected as it was a feat achieved in challenging circumstances or was it a case of going overboard as a good number are yet to be fully vaccinated?

It is true that the circumstances were and continue to be challenging. As for a 100-crore mark, it will come eventually if you keep vaccinating; in that sense, it is akin to celebrating birthdays. If you live long enough, you will eventually become, say, a sahasrachandradarshanik (a person who’s lived 1,000 full moon days). Some amount of feel-good celebration is useful in maintaining morale, I suppose, but when the occasion is used, as you point out, for bragging unrestrained by any connection to the sobering realities on the ground, it is liable to bring dangerous complacence in its wake; witness urban India’s crowded and mask-less festival marketplaces.