Herd immunity, what the experts say

Vaccinations against Covid, will herd immunity be achieved? And when? Scholars debate the question with different positions. To achieve herd immunity “I would tend to say them by the summer, staying wide for prudence between August and September” said yesterday the president of the Superior Health Council (Css) and coordinator of the Cts Franco Locatelli, guest of e- Winds on Sky TG24. “Already in June – he added – we will have more than 20 million doses available” of the anti Covid vaccine, “which divided into a daily count brings us to a figure between 650 and 670 thousand doses per day. By continuing at this rate we will certainly be able to further reduce the circulation of the virus ”. According to virologist Fabrizio Pregliasco, herd immunity “will never reach it. It is in fact the condition in which, according to mathematical models, the spread of the disease is eliminated, and we do not succeed, in the sense that the disease will become endemic. we will be able to lower the incidence a lot and therefore to live with the virus. And this we will be able to do within 2-3 months “. The virologist of the University of Milan at Adnkronos Salute explains how “even reaching 80% of the vaccinated population”, a target recommended as the WHO Europe vaccine coverage target, “the disease is almost extinguished but it never reaches zeroing of virus circulation “. “When we reach 50% of vaccinated people, to which we add about 4 million of those recovered who – underlines Pregliasco – are actually at least double, because there are many who are not registered as sick in the first wave, we will get to have the frail elderly protected, but there will remain a quota of young people who will keep the chain of contagion ‘active’. So, thanks to vaccines, we can talk about coexistence with the virus for a few years, which hopefully – he concludes – will be a very ‘civil’ coexistence. ” ‘herd immunity depends on the combination of natural immunity with vaccine immunity – explains Pier Luigi Lopalco, epidemiologist and health councilor of the Puglia Region to Adnkronos Health – It is therefore difficult to give a level of coverage that indicates herd immunity because: we do not know the exact proportion of people who have had the infection and many people who have had the infection have also been vaccinated, so there is some overlap between the two populations “. “We know that with 80% of the immune population the circulation of the virus stops. But to reach this goal we must also vaccinate minors. At this moment the aim of vaccination remains to protect the most fragile population from serious forms of disease “, concludes Lopalco. For Andrea Crisanti, director of the Institute of Microbiology of the University of Padua,” it is not absolutely certain that herd immunity against Covid will be achieved. If children under 18 are not vaccinated it will be difficult to obtain it . We also do not know when this immunity lasts, we do not have precise data. And if it lasts only 8 or 9 months, the carousel starts again, it will be necessary to immunize several million people a month. In any case it is not a fundamental goal, in the sense that even if not it is reached, but close to close levels, the positive effect of vaccination will be the same “. The really important thing, continues Crisanti at Adnkronos Salute, is instead that “the elderly are vaccinated. Thus the social danger of the disease decreases, reducing serious cases, deaths and pressure on health facilities”. We need to have realistic perspectives but able to protect the fragile. “Here in England – says the virologist who works between Padua and London – they have vaccinated over 70% of the population with a single dose. And in any case, there have been many cases for 5 and a half months and herd immunity has not yet been reached. “. In perspective, according to the virologist, “we will necessarily go towards an endemic presence of the virus. Eliminating it completely, at this point, is impossible. It is very difficult to eradicate a pathogen, we have only succeeded for smallpox and we are close to polio. And it took tens of years “, he concludes. Herd immunity? “In Italy at the end of August, the first half of September, by vaccinating at least 65% of the population, we will be able to achieve ‘solidarity or social immunity’, that is, we will have secured even people who cannot be vaccinated, and we will be able to afford reopening and socialization “says to Adnkronos Salute the immunologist of the Policlinico Umberto I in Rome, Francesco Le Foche, who underlines how the concept of herd immunity should be ‘reviewed’ in new terms. In fact, the expert expands the concept “which today – he says – must be conceived in different terms from the past, as in the globalized world, where we move very quickly, as demonstrated by the virus, which has transformed a Chinese epidemic in a short time into a pandemic, herd immunity must provide for a planetary immunity. That is: we must vaccinate others to protect everyone. It is a bit like the immune system – he explains – which protects the species and not the individual but protecting the species protects the individual. The same must happen globally: we protect others, we protect everyone to protect ourselves too “, he concludes. “According to the current anti-Covid vaccination plan we cannot achieve herd immunity – says Stefania Salmaso, independent epidemiologist of infectious diseases to Adnkronos Salute – And it is not a goal that can be pursued in the short term. We are vaccinating for age groups. and the protection that could be provided by the ‘flock’ occurs when there are so many vaccinated people in the population that indirectly protect even those few who are susceptible from contagion. In Italy instead of susceptible to ‘contagion’ there are still many ‘. “It is clear – he adds – that vaccination greatly contributes to reducing the negative effects of infections, therefore the number of deaths and hospitalizations in intensive care but infections will continue to circulate among young people. herd immunity. However, we will content ourselves with reducing hospitalizations and deaths and lowering the incidence with other countermeasures “. And in the future? “It depends on the vaccination strategy – Salmaso replies – because when it is decided to vaccinate all children and young people, having made the necessary risk-benefit assessments, it could be conceivable” the objective of herd immunity. “But – he observes – since we all know that there is a threat of variants that for now are ‘recognized’ by vaccines, but in the future this may no longer be the case, then, even in the future, herd immunity cannot be a bulwark. So – he concludes – at this moment it does not seem appropriate to talk about it “.