How can we achieve this objective, so simple and yet so difficult? Of many ways. For example, limiting contacts between people, as we did through confinement. We can also reduce the probability of contagion in existing interactions, through masks and distancing. A third route is immunization, by vaccination or by so-called wild-type immunity.
Group immunity is based on the idea (purely statistical) that when a sufficiently high number of people have overcome the disease, its transmission is stopped. This is so because each patient encounters a smaller number of people susceptible to being infected (because many are already immune).
Is this strategy viable? Can it be implemented at the regional, national or even global level? The idea is not new. Since the beginning of the pandemic, some countries have opposed measures to curb infections. In the end, the health collapse of the first wave made them change their minds.
In recent weeks, however, it seems that memory is beginning to waver. Probably due to the threat of a devastating economic crisis, the group immunity hypothesis has been reborn from its ashes.
A group of experts published the Great Barrington statement on October 4, rejecting the confinement and distancing measures due to their social and economic consequences. They argue that most of the world should “live normally” until they achieve group immunity. The most vulnerable fraction of the population should, according to them, self-isolate during this period. They have dubbed this strategy “targeted protection”.
Another group of experts quickly responded against this statement by publishing the John Snow manifesto, which takes its name from the considered father of modern epidemiology. For them, the pursuit of group immunity is a bad idea.
These are the reasons:
– Millions of people would die
The lethality of SARS-CoV-2 is not known for sure and also depends on the moment and the population observed. Even so, conservative estimates are around 0.6% of infected deaths, which would imply that, if herd immunity is of the order of 60-70%, some 200,000 people would die in Spain. Zas, Santander or Castellón removed from the map! Not to mention the aftermath of many of the patients who manage to survive.
In addition, the health collapse due to the high percentage of patients requiring hospitalization would imply that not only Covid patients would suffer, but also other pathologies that could not receive the necessary care.
This would have profound social and economic consequences. Even without appealing to group immunity, the collateral mortality to Covid would have unacceptable dimensions.
As if this were not enough, we would have another problem.
– We do not know if we would achieve group immunity because we are not clear about how individual immunity works
For group immunity to be achieved, we would need between 60 and 70% of the population to be immune at the same time. Not only do you not get sick, but you also cannot pass the virus to others.
However, we do not yet know how immunity works or how long it lasts. Antibodies, which are the part of the immune response that we have studied the most, disappear after a few months, especially in mild cases.
Furthermore, we know that reinfections are possible, which could be an insurmountable obstacle to obtaining group immunity.
– Targeted protection is not only ethically debatable: it also has technical difficulties
It is extremely difficult to effectively isolate the elderly and vulnerable groups ( Could they not receive any visitors and would they be condemned to live in solitude? What happens to the nursing home staff? their workplaces? Would we isolate them too? ).
In addition, it is not so easy to define the vulnerable population: many young people, apparently without previous pathologies, have suffered serious cases of Covid, and we have no way to identify this population at risk: it could be anyone. In fact, taking into account the excess mortality data, during the first wave 25% of the excesses occurred in people under 65 years of age.
– Group immunity estimates are based on debatable mathematical models
Typically, herd immunity is calculated as (1-1 / R₀) x100), where R₀ is another concept that has entered our lives during the pandemic: the so-called basic reproductive number.
But these estimates are based on simplified models that not only do not allow accurate predictions, but also ignore the role of superpropagators.
In such a way that we do not even have guarantees that if 80% are infected, the epidemic will stop and will not affect the remaining 20%.
If these keys are so clear, why is support for group immunity resurgent?
Most of the countries live in a state of continuous restriction or under the shadow of a new massive confinement. This threat adds to the impression that all the effort made in the previous months has been in vain, or to the anguish of jobs lost or at risk. The desire to regain normalcy is also fueled by a damaged economy that imposes increasing pressure to seek alternative solutions.
However, the consequences of letting the pandemic evolve uncontrollably would be even more devastating than the effect of the measures. We need to design rational strategies that protect both public health and the economy and our lifestyle.
This can only be done through an ethical debate on individual responsibility, a climate of coexistence and community, total transparency about the data on the evolution of the pandemic ) and the reasons that support the decisions made.
In short: data, science and prudence. We must select the measures that best suit our objectives, but not imposing any would be the worst idea of all.
Sara Lumbreras, Professor and researcher at the Institute of Technological Research, Comillas Pontifical University and Mario Castro Ponce, Professor and Researcher at the Higher Technical School of Engineering (ICAI), Comillas Pontifical University
This article was originally published on The Conversation. Read the original.
