Covid and herd immunity, is it possible? What do Bassetti, Gismondo, Pregliasco say

Is it possible to achieve herd immunity with covid? While the infections increase as well as the positivity rate, with the virus continuing to mutate, the experts – from Bassetti to Gismondo, Pregliasco and Ricciardi – answer the question of whether or not it is possible to achieve this goal. Bassetti “Herd immunity will never be achieved because the” Covid “virus continues to mutate. We learned about it with a virus that was always the same and with a vaccine that was able to significantly reduce infections and serious illness, for example that of measles. However, we cannot use the expression herd immunity for Sars-CoV-2 because it is a respiratory virus that continues to change, while the R0 of measles has always been 18. While with Sars-CoV-2 it was first 2, then 20 and maybe tomorrow it will be 30. We need to think about immunity for severe forms of Covid disease and we have already achieved this “. Matteo Bassetti, director of the Infectious Diseases Clinic of the San Martino Polyclinic in Genoa underlines this to Adnkronos Health. Bassetti explains why we have immunity to the severe form of disease associated with Sars-CoV-2: “Among those who are vaccinated with triple dose , plus those recovered from Covid once or twice, each time we put an extra stake and an extra defense against the initial highway with which the virus entered the lungs. Today the virus enters us less and we are faced with immunity against the severe forms of Covid disease, I would say 98-99% of the population “, estimates the infectious disease specialist. Gismondo Whether or not herd immunity remains a utopia against Covid-19, “it is not possible to predict it now”, because “it will depend on future mutations of the virus. And in any case, natural immunity will always be higher than that conferred by old vaccines “. So at Adnkronos Salute Maria Rita Gismondo, director of the Laboratory of clinical microbiology, virology and bio-emergency diagnostics at the Sacco hospital in Milan. But “we – she adds – we can always look at the history of the pandemics, which ended only when the virus spread, immunity was created and most of the population found themselves protected”. It is precisely in the hope that history will repeat itself that “I believe – reiterates the microbiologist – that in this phase in which Sars-CoV-2 is spreading so significantly, we can expect that the population will remain immune and that the pandemic can end. I repeat – Gismondo is keen to specify – it is an expert’s thinking based on what is the knowledge and what is the history of pandemics. If this virus behaves differently, I certainly cannot predict it “. Pregliasco “Not a herd immunity intended as zeroing” of the possibility of getting infected, but “an immunity intended as a periodic reduction in the share of the population susceptible to infection”. Considering the changeability and unpredictability of Sars-CoV-2, “wave immunity” is the only possible one against Covid-19 according to virologist Fabrizio Pregliasco, professor of Hygiene at the State University of Milan and health director of the Irccs Galeazzi. On this type of immunity, explains the expert to Adnkronos Health, we can act by regulating the length of the ‘good waves’, those with a larger slice of the protected population, through vaccination and prudent anti-contagion measures. form of immunity to which it is realistic to aim for having to live with Covid, Pregliasco returns to refer to the epidemic trend made up of “rising and falling waves that we are witnessing, waves like those created by a stone thrown into a pond”, he reiterates . That is, there will be periods like this, with “Omicron 5 super contagious, a large share of the population susceptible to infection and the ‘taps’ of very open movements and social contacts”, and subsequent periods in which “for 4-6 months from infection or vaccination a greater proportion of subjects will remain immune “. And then “still new variants in which the share of susceptible people will be greater, which will once again be reduced with vaccinations and / or natural infection”. According to the virologist, it will therefore be “a bit like with the flu, which does not affect the same people every year, but those who are not immune because they are not vaccinated or because they have not had it for a while”. A wave immunity, in fact. Vaccination aside, Pregliasco invites you to always pay attention to the “contact taps: you must always be on your guard, because if you open the hot water suddenly it is easier to burn yourself and you find yourself with a quantity of simultaneously sick subjects difficult to manage “. Ricciardi Herd or population immunity, “with a virus that causes so many reinfections, is not technically possible”. You can have, in people who become infected, “a momentary refractoriness, but that lasts a few months. With germs so contagious and, above all, that have the ability to infect again, there is no possibility”, he tells Adnkronos Health Walter Ricciardi, Professor of Hygiene at the Catholic University and advisor to the Minister of Health Roberto Speranza. Herd immunity, explains Ricciardi, “is acquired when you get permanent immunity, thanks to a vaccine or a natural infection . With Sars-CoV-2 this does not happen precisely because it is extremely contagious and able to reinfect “. Lopalco “With Sars-Cov-2 there will be no population immunity. The characteristics of this virus – that is the ability to evade the immune system and produce repeated infections, together with the fact that there is an animal reservoir – clearly indicate that the viral circulation is not it can never be stopped. But we experts knew this from the start. ” The epidemiologist Pier Luigi Lopalco, professor of Hygiene at the University of Salento, explains this to Adnkronos Salute.

La Vecchia The herd immunity project to defeat Covid-19 turned out to be “the great disappointment”. “When we first went for the vaccine, we all hoped we would achieve it, reaching 80% coverage first, then 90-95% coverage. As with measles, we hoped the disease would go away. However, this was not the case, the target was corrected upwards “while passing” from variant to variant “, but for” nothing “. And “the ‘drama’ for herd immunity, the one that dismantled the initial plans, was the Omicron variant”. The epidemiologist Carlo La Vecchia, a professor at the State University of Milan, traces what appears to be a doom for the dream of a definitive anti-Sars-CoV-2 shield at Adnkronos Salute. “those infected with Omicron 1 can re-do Omicron 2 and then Omicron 5. If they continue to develop sub-variants that do not respond to the immunity acquired by the previous sub-variant or by the vaccine – continues La Vecchia – herd immunity will not exist. like all viruses, but we are looking far, even Sars-CoV-2 will stabilize at some point. Today, however, this is a new virus that continues to vary. It is possible that it stabilizes, but unfortunately every 2- 3 months we had a sub-variant that was able to infect both the vaccinated and those who had made the previous sub-variant “.