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New variants of the coronavirus make herd immunity an unattainable goal in the short term | Society

Herd immunity, that philosopher’s stone that was to turn the pandemic into a memory, is a goal that today seems distant. Perhaps unattainable. As the new variants of the virus are increasingly infective, not only is it moving away from that 70% of the immunized population that was calculated at first, but it is practically impossible to reach it in the short term. Although it is not known exactly what the new figure may be, experts place it around 90%, a number that cannot be reached without vaccinating children under 12 years of age, for whom there is still no approved drug and that in Spain they make up 11% of the population.

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The idea of ​​group protection is not only theoretical: it keeps diseases such as measles and diphtheria at bay and managed to eliminate smallpox, the great infectious disease that humanity has eradicated. It is based on the fact that when a sufficient number of the population is immune to a virus, this particle is left without the ability to spread. If a person becomes infected, but the vast majority of those around him are not susceptible to being infected, he will not be able to jump to another organism and will disappear in the patient: either by killing him or at the hands of his immune system.

The percentage of population required to reach herd immunity depends on the infective capacity of the virus. And in SARS-CoV-2 it has grown to the delta variant, the most contagious to date. A report from the United States Center for Disease Control, to which he had access The Washington Post, points out that each person can infect nine others, three to four times more than was originally estimated, making it as contagious as chickenpox. And, in parallel to this greater transmission capacity, the estimates, always approximate, of the percentage of the vaccinated population necessary to achieve herd immunity rise. If at the beginning there was talk of 70%, all the experts consulted consider that threshold has been exceeded, and those who get to specify it raise it to around 90% or more.

For example, epidemiologist Javier del Águila believes that the idea of ​​herd immunity “does not seem very realistic in the current context.” “Quite a few epidemiologists around the world have been dealing with the subject for a few months. It comes from more classic diseases, such as chicken pox, measles, smallpox. Covid is very different, being a respiratory virus with such high transmissibility, several problems are linked: coverage rates close to 95% would be needed. This is something very difficult, even in countries like Spain, where reluctance to vaccinate is very low ”. This is coupled, he adds, to the fact that variants such as the delta trigger the curve when they find a group of susceptible people. “And when there are many infected, as the vaccines are not perfect, it also ends up reaching those who have the complete pattern,” he ditch.

José Jiménez, researcher at the Department of Infectious Diseases at King’s College London, goes further and believes that it would be better not to set percentages of group immunity, a goal that, he says, it is not known if it can be reached and that, in any case, go far. “They are very theoretical estimates and can vary greatly depending on the effectiveness of the vaccines and the appearance of new variants. The best message we can give is to vaccinate as much as possible without setting any percentage as a goal, ”he says. Vaccination will ensure that the vast majority of cases are mild or asymptomatic; also so that the next epidemic waves are much less bulky and so that the coronavirus ceases to be the social problem that it has posed until now. But probably not, at the moment, to completely stop the spread.

A similar argument makes Ignacio López Goñi, professor of Microbiology at the University of Navarra: “Perhaps, instead of obsessing over numbers, about group immunity, it is more realistic to set the objective of reducing health collapse. If there isn’t, we could all go back to the closest thing to normal. We are not going to eradicate the virus, we will have to live with it, probably. For that, you have to vaccinate the most vulnerable. But the virus will move where we leave it, now especially in the unvaccinated ”.

A queue to get vaccinated at the Isabel Zendal Hospital, in Madrid, on July 7.
A queue to get vaccinated at the Isabel Zendal Hospital, in Madrid, on July 7.David G. Folgueiras

The most likely, in the opinion of Miguel Hernán, Professor of Epidemiology at Harvard University, is that the coronavirus will become endemic, as it happens with others. These types of pathogens are what cause colds. “Possibly, in their day they were a pandemic and today there is no epidemiological surveillance of them because it is not necessary,” he says. The trend of the covid will be this if there are no mutations that make the virus escape the protection that vaccines provide against the most serious forms, as more and more people have some type of antibodies, either due to having received the puncture or because of being infected. That is, at least, what this expert considers more plausible, who clarifies that problems will come for people who for some reason do not generate defenses.

This is in addition to the fact that approved vaccines, although they are very good at preventing the most serious variants of the disease, do not completely prevent transmission. At the moment, there is no consensus on their ability to protect against delta variant infection. This same report indicates that although infections among those vaccinated are still rare, when they occur they have the same transmission capacity as an unvaccinated person.

With all this, it would even be doubtful to achieve herd immunity by vaccinating all those over 12 years of age. And reaching this goal is practically impossible. According to the latest survey by the Spanish Foundation for Science and Technology (Fecyt), the number of people who flatly refuse to inject themselves is 4%. To these must be added another portion of the population that cannot be pricked due to health problems, another that the system does not reach, another that, without being directly against it, does not bother to go for the injection or prefers not to do so. . In short, exceeding 80%, without mandatory vaccination, something that is not being considered for now, will be really complicated.

The ethical debate of vaccinating children

In order to reach 95% percentages like the one described by Del Águila, it would also be essential to vaccinate children. But even when there is a vaccine for them, there will be an ethical debate that is difficult to resolve. As age decreases, the risk-benefit balance of vaccines decreases, since the severity of the disease also decreases. Although the chances of a serious side effect from a needlestick are remote, in children under 12 they are probably greater than those with infection. Countries like the United Kingdom have even ruled out vaccinating adolescents, for whom there is an approved injection, for this very reason.

Federico de Montalvo, president of the Bioethics Committee of Spain, explains that vaccination seeks individual and collective protection. “Would it be ethical for children to take a risk to protect society while there are adults who do not get the vaccine because they do not want to?” De Montalvo believes that when that time comes, the debate on mandatory vaccination in adults will have to be resumed, which until now is not on the table.

Another derivative is that even if Spain, with its good vaccination rate, achieved a supposed herd immunity, the rest of the world will take time to do so. Other Western countries are having serious obstacles to advance, as is the case with the United States, which is looking for all kinds of incentives for the population to be immunized. Even Israel, which began as a world leader, has been stagnant for weeks at around 60% of people with complete guidelines, a figure that Spain will reach in a few days. But these are first world problems. For developing countries, where doses are barely reaching and with very weak health systems, group immunity is a pipe dream.

In Del Águila’s opinion, one should be more concerned with providing vaccines to these countries than with a third dose in the rich, as some are already doing, such as Israel itself. “As the virus circulates around the world, it will have more capacity to mutate, and the more it does, the more likely it is to escape vaccines,” he says. This is the great fear of public health experts. As long as punctures continue to prevent hospitalizations and deaths as they do until now, a high number of vaccinated people will keep the disease at bay, even without group protection. But if a variant circumvents this barrier, strong measures will again be necessary to prevent health systems from collapsing again.

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