Covid vaccines and variants, the ‘lesson’ of Roberto Burioni. The virologist, a professor at the San Raffaele University, breaks the silence on Twitter by publishing an ‘didactic’ thread on the topic of the moment: covid vaccines, their effectiveness, the risk represented by the variants and in particular by the Delta variant. “Do vaccines cause the emergence of resistant variants? A few days ago I heard on the phone a dear friend of mine, Pietro Spagnoli, who asked me this question, which has no simple answer at all”, Burioni begins. “Since Pietro is not only a friend, but he is also the singer who gave me the best Bartolo of my life (Rossini Opera Festival 2018) because he finally represented him not as a good-natured mocked, but as an evil villain, I absolutely have to answer him hoping to do something pleasing to all of you “, is the prologue.” A virus (forget how) passes from an animal to man. If it happens in the world without vaccines this virus begins to mutate (we have already said how) and mutations that give the virus an advantage (which typically consists of greater contagiousness) begin to emerge and take over, “says Burioni.” At some point the virus will reach maximum contagiousness, it will infect most of the inhabitants of the Earth and then it will give periodic epidemic waves infecting the newborns, not immune, when they have reached a number such as to sustain an intense viral transmission. This happened for measles, for rubella, for hepatitis A and for many other viruses: we have already found them beautiful and evolved centuries (or millennia) after their passage to man “, underlines.” The coronavirus did exactly the same thing: in March 2020 a first variant that quickly took over, then came the alpha variant (English) that was transmitted more and became the dominant one, now there is the delta that is even more contagious than the alpha one and is quickly taking its place. As a consequence, the current virus is very different from the one that circulated last year: the virus is immensely more contagious (let’s take this into account when we think about the opening of schools) “, he continues.” At a certain point – the excursus continues- is arrived in record time and in the midst of the pandemic, for the first time in the history of man, a very effective vaccine. At this point, the convenient variant for the virus is no longer only the one that spreads the most, but also the one that manages to infect the already vaccinated. Such a variant, in the absence of a vaccine, would have no advantage and would never emerge “.” But in the presence of vaccinated it could emerge. So, in a sense, it is carpet vaccination that creates the conditions under which a resistant virus could emerge. However – he warns – do not make the mistake of considering this a negative effect of vaccines: without vaccines the variant could not emerge simply because it would find the free path towards infecting the whole world. The vaccine is an obstacle that the virus TRIES to overcome with a variant. Will he succeed? We cannot know this. “” Until the moment I write these lines, a variant capable of escaping the vaccine has not emerged, and nothing suggests that it could emerge, and if it did emerge it could be less pathogenic and / or less contagious, “he says. Burioni. “But since predicting the future is not one of the tasks of a scientist, more can not be said. What, on the other hand, can be said with certainty? That to generate variants the virus must replicate by infecting people. Every person infected with the virus makes a roll of the dice that might suit them, generating a vaccine-resistant variant, “explains the professor.” So actually, the best strategy we have to prevent vaccine-resistant viral variants from emerging is vaccinate everyone as soon as possible in order to prevent the virus from replicating, and to try to cheat us “.