Wednesday, October 20

Why achieving group immunity is not feasible and we will have to continue living with the coronavirus

Spain begins to leave the pandemic behind. Asturias has been the first community to fall below 25 cases of incidence, the threshold associated with the new normal in the COVID traffic light in Health, pending update. The Navarrese Government, with the double, considers that the epidemic circulation of the virus has been put to an end to make way for the “probable” incorporation of the coronavirus in the list of infections that are transmitted endemically. It is the scenario that, according to the experts consulted, is going to take place in the coming weeks throughout the Spanish territory.

Epidemiologists and immunologists rule out group immunity with the available scientific evidence on the behavior of the virus. The novelty is that they agree that it will not be necessary to return to a normal life. “Achieving sufficient immunity to eliminate the disease is not feasible with what we know, which does not mean that with a highly vaccinated population a barrier immunity is achieved that allows transmission to remain at low levels”, exposes Pere Godoy, president of the Spanish Society of Epidemiology. Vaccine coverage already exceeds 75% in Spain.

Group or herd immunity is a term that became popular as vaccination progressed. It was envisioned, at first, as a possible target. It would be reached, then set the scientific criterion –which is also evolving with the advance of the pandemic–, with 70% of the inoculated population. The President of the Government, Pedro Sánchez, affirmed on May 10 that Spain was “100 days” away from achieving it. So this situation was linked to the end of the virus.

The theoretical basis for the concept arose in a discussion of measles in the early 20th century, but the precise definition was established in the 1970s. “It is a point from which there is so much immunized population that the possibility of someone infecting a person around him is very short, “explains epidemiologist Pedro Gullón.

Source: Ministry of Health (data updated to )

The classic concept, as defined by Fox, Gullón continues, implies four requirements: that the only reservoir is the human being, that transmission occurs by direct contact, that the vaccine provides robust immunity, and that the distribution is random. . “We know that at least two of these characteristics – the reservoir and chance – are not met. We are not clear about immunity, we know that the disease reduces its severity, but it can continue to transmit. It is not cut off,” he adds.

Alfredo Corell, president of the Spanish Society of Immunology goes further. “Even if 100% of the population were vaccinated, the virus would not disappear,” he assures in conversation with “The undeniable achievements in vaccination coverage have freed us from further collapse of care, more severe disease episodes, and more pronounced mortality, but […] they are not enough to generate group immunity, which is increasingly unlikely given the characteristics of the disease and the nature of the vaccines, “indicated this article by Daniel López Acuña and José María Olmos published in in August. The experts asserted then that group immunity linked to a vaccination coverage of 70% of the population with the complete regimen was “illusory”.

Why then was the threshold set at 70% of vaccination coverage? Why then was it increased to 90%? The calculations were made with the assumption that immunity would last, according to experts. The formula was made taking into account that R –the potential for the spread of the virus– would be equal to 0. In the case of 90%, the new variants were introduced in the calculation.

The recommendation of epidemiologists is to avoid thinking that there will be a time when there will be no transmission. “The same is true because it is so extremely small that … but it is tremendously complicated. One should not give false hope that there will be no cases. It will be necessary to keep an eye on it, considering that the increase in transmission will not necessarily be accompanied by an increase in the restrictions “, deepens Gullón.

The Alerts Report of the Ministry of Health is immersed in the update of the COVID traffic light, approved a year ago, to establish the different levels of risk and a series of recommendations associated with each one. The epidemiological scenario at that time was radically different from now. The General Directorate of Public Health of Cantabria has announced that it is considering making a change in the parameters it uses to mark the restrictions against the coronavirus to consider more hospital admissions instead of the accumulated incidence, since infections will continue to occur although the population is vaccinated and its effects will be minor. All communities continue, some faster than others, raising limitations.

Leave a Reply

Your email address will not be published. Required fields are marked *