Herd immunity is continually debated in the ever complex discourse of COVID-19. Serosurvey results from across the country indicate spread of the contagion across urban and rural areas, more so in the urban and particularly among slum populations. The common question with evidence of substantial spread is if we are closer to herd immunity. Experts wonder whether the recent surge in cases in Delhi is attributed to a lowering of guard by policymakers, administrators and communities alike, based on such expectations.
The conventional wisdom of herd immunity is that it marks the end of the epidemic. Originating in veterinary public health, it entered the lexicon of human health epidemiology exactly a century ago in the context of explosive diphtheria outbreaks; but battle lines have never been drawn among researcher-practitioner and policy communities with pointedly political implications as at present. When one infected person in a population leads to less than one secondary case on average, which corresponds to the effective reproduction number R (that is, the average number of persons infected by a case) dropping below 1 in the absence of interventions, herd immunity is considered to have been achieved.
In the March-April phase of the pandemic in France, it was estimated that the herd immunity threshold for SARS-CoV-2 was expected to require 67 per cent population immunity. Another way of understanding this is at the current level of about 10-15 per cent of the global population showing evidence of infection, most of us remain susceptible — nearly 5 billion shall need to have the infection to achieve herd immunity.
Some of the recent debate was sparked by the recent Great Barrington Declaration (October 4) by a group of infectious disease epidemiologists and public health scientists who recommend “focused protection” to offset some of the negative damaging physical and mental health consequences of current COVID-19 management policies, in specific lockdowns and related restrictions. They proposed a “compassionate approach that balances the risks and benefits of reaching herd immunity” to allow those who are at minimal risk of death to live their lives normally to build up immunity to the virus through natural infection, while better protecting those who are at highest risk.
The WHO director-general responded in his press briefing on October 12 that herd immunity is achieved by protecting people through vaccines and not by exposing them to disease which in his view is “scientifically and ethically problematic”. This was further contested by another group of scholars, who proposed the John Snow Memorandum (October 14). Acknowledging that lockdowns while being necessary are disruptive and that their consequences have generally been worse in countries unable to leverage the lockdown phase to establish effective pandemic control systems leading to “widespread demoralisation and diminishing trust”, they argued that uncontrolled transmission (the herd immunity approach) in younger people entails significant risks of morbidity and mortality across the whole population. Donald Trump, during his election campaign, largely avoided using the term “herd immunity” but his advisors are fairly strong advocates that are reflected in the policies.
The fact is that both scientific and moral judgement matters. Ethicists point to the paradox in the Barrington Declaration that the elderly have not really been protected in the real-world experience, despite efforts to do so. Further, the elderly shall also need treatment, entailing substantial resources (more so in overloaded health systems), and some of them shall survive with long-term sequelae (long COVID). Proponents of the declaration urge that people should think of trade-offs at a “communitarian” level implying that the young and healthy shall contribute to the societal cause by becoming infected (COVID outcomes can be unfavourable in the young too, with relatively high levels of co-morbidities in the Indian context).
Communitarianism is a complex concept, the core being that human identities are shaped by different kinds of social relations in communities that shape our moral and political judgments and that we have a strong obligation to support and nourish communities providing meaning to our lives. It may be surmised that while the opponents of the declaration conform to the ethics principle of “first do no harm”, the signatories were upholding the decline of valued forms of community, viewing the current crisis through a humanitarian and policy lens rather than a medical or clinical lens.
India’s current approach is to continue with limited restrictions with hopes of early rollout of vaccine as the key strategy. Lockdowns have in many instances not led to the promised normalcy at the end of it. A case in point is the slew of emergency interventions by the Centre now to augment clinical care, including airlifting additional doctors and paramedical staff from the central armed police forces and providing hospital equipment from central resources to support the Delhi government. Japan and Vietnam are models of successfully handling the situation through pragmatic and rigorous public health practices; an “adaptive model” in which there are substantial changes in the health system organisation and its responses appropriate to time and context as the pandemic develops.
The COVID-19 situation underscores the importance of combining good science with prudent judgment to meet the needs of large populations, while maximising scientific quality in the face of applicable limitations and competing interests. Most countries professed several policies to address vulnerabilities, but implementation challenges abound. The task of medical scientists and public health researchers is to continue to unpack a nuanced understanding of vulnerabilities; the politician (as Rudolf Virchow put it), “the practical anthropologist, must find the means for their actual solution”.
This article first appeared in the print edition on November 17, 2020 under the title ‘War against virus’. The writer is chairperson at the Centre of Social Medicine & Community Health, Jawaharlal Nehru University
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