Plan B for Covid-19: a Statistical Analysis of Herd Immunity

| Press release

A study from EconPol Europe which uses standardized guidelines to identify ‘optimal’ herd immunity policies reveals transferring the risk from the old to the young could reduce a global death toll by over 80%.

But the moral concerns related to such a policy “would go against several decades of policy evaluation practice in which all lives are equally valued,” says the study’s author Christian Gollier, (EconPol Europe, Toulouse School of Economics, University of Toulouse-Capitole).

In the absence of a treatment or vaccine, the study examines the two options available for managing Covid-19: long confinement of a large proportion of the population and the associated economic costs (Plan A), or to progressively build herd immunity by exposing the population to the virus (Plan B). But, says Professor Gollier, attaining herd immunity requires governments to expose a fraction of the population to the virus, and to recognize that some people in this targeted population will die.

“Determining who should be exposed to the virus to attain the herd immunity is a crucial policy issue,” he says. “Which criteria should be used to perform this task? Should we leave nature do its dismal work at random until the natural immunity be obtained, or should we protect some specific communities from this danger?”

The Covid-19 infection-fatality ratio is 0.002% for individuals younger than 10 years old, rising to 9.3% for people aged 80 and over. “Given this 4650-fold difference in mortality risk, it may be desirable to expose less vulnerable people first in the hope of building the herd immunity before relaxing the protection of the more vulnerable people,” says Professor Gollier.

Taking France as an example, the optimal deconfinement strategy would be to deconfine all people aged 65 and younger (100% of the 0-59 class, and 55.47% of the 60-69 class). This partial deconfinement based on age will lead to total number of deaths of 59,704 people, compared with 446,792 persons with total deconfinement.

However, 32 more individuals under the age of 20 will die under this ‘optimal’ policy compared to the non-discrimination policy. 

And although he is keen to stress that transferring mortality risk across individuals raises complex moral issues and constitutional concerns, Professor Gollier says that the right to a safe life is already “vastly discriminated” due to exposure to pollutants and access to efficient health services.

“Rather than considering health protection as a basic human right, the practice of public decision-making has been to allow for tradeoffs between individual health and collective wealth. Standard guidelines such as Value of Statistical Life and Quality Adjusted Life Year for public benefit-cost analysis most often require a specific system of values to account for the impact of public policies on mortality risks.

This value system has routinely discriminated against specific individual characteristics such as age and morbidity. Transferring some mortality risk to less vulnerable people may not be socially desirable if society values the lives of these less vulnerable people more. This may be the case, for example, if vulnerability is positively correlated with age, because preserving the life of a young person is commonly considered as more valuable than preserving the life of an older person. In this paper, I use the existing statistics of Covid-19 mortality rates for different age classes to determine the optimal targeted deconfinement for the most common ethical attitudes towards the preservation of different lives.

“I don't have a solution to break this moral dilemma,” he adds. “My aim in this paper is to quantify the consequences of different social norms used in the current context, as measured by the number of people who are expected to die, or by the number of life years lost.

“Transferring the exposure from the old to the young reduces the death probability by a factor 1000, but moral concerns could reverse this recommendation only if society values one young life more than a thousand lives of people aged 65 years or more.”

Read the full paper: