The Delta variant of the coronavirus is nearly 6 times less sensitive to antibodies developed by people cured of Covid-19, and up to 8 times less sensitive to vaccination-induced antibodies. This is what emerges from a study conducted in India and the United Kingdom and published in ‘Nature’, which investigated the reasons why the mutant of Indian origin managed to become prevalent, also supplanting the previously dominant Alpha variant. In addition to having a greater ability to escape anti-Covid antibodies, Delta also appears to be more effective at penetrating inside respiratory cells and replicating once inside. Among the main authors of the work is Ravi Gupta, of the Cambridge Institute of Therapeutic Immunology and Infectious Disease at the University of English Cambridge. “By combining laboratory tests and epidemiological analyzes – explains the scientist – we have shown that the Delta variant is more capable of replicating and spreading than other mutants” of the new coronavirus. “There is also evidence that neutralizing antibodies produced following previous” Sars-CoV-2 “infections or” anti-Covid “vaccinations are less effective in blocking this variant.” It is therefore “likely that these factors contributed to the devastating epidemic wave experienced in India during the first quarter of 2021, with about half of the cases involving people already infected with other variants before”. the immune response, the researchers used serum extracted from blood samples taken from people of a UK cohort, cured of Covid-19 or vaccinated with products from Oxford / AstraZeneca or Pfizer / BioNTech. They thus calculated that the Delta variant, compared to Alfa, was in fact 5.7 times less sensitive to the sera of previously infected people and up to 8 times less sensitive to the sera of the vaccinated. In other words, an 8 times higher level of vaccine-induced antibodies would be needed to block the ‘Delta version’ of Covid. In line with this observation, the results of the examination of over 100 infected health workers in 3 hospitals in Delhi, almost all vaccinated against Covid: in these operators, Delta was transmitted among the immunized to a greater extent than Alfa. Using three-dimensional airway organoids – mini-organs grown from cells in this tract – the scientists then studied what happens when the virus reaches the respiratory system. Working safely, the team used both live coronavirus and a ‘pseudotyped’ virus – a synthetic form of SARS-CoV-2 that reproduced key mutations of the Delta variant. The researchers found that Delta was more efficient in making its entry into cells and, once it entered, it replicated better. Factors that, together with the ability to evade immune defenses, would have given the mutant an evolutionary advantage. “The Delta variant has spread widely to become dominant around the world because it is faster to spread and infects better than most. other variants – comments Partha Rakshit of the National Center for Disease Control in Delhi, joint senior author of the work – It is also better at bypassing immunity induced by previous exposure to the virus or vaccination, although in these cases the risk of moderate to severe disease is still reduced. “” Infection of vaccinated healthcare professionals due to the Delta variant is a significant problem – warns Anurag Agrawal of the Csir Institute of Genomics and Integrative Biology in Delhi, joint senior author – Although they may experience only one mild form of Covid, are likely to infect people who have suboptimal immune responses to vaccination due to particular health conditions and these patients could be at risk of serious illness “. According to the expert, “we urgently need to consider new strategies to increase responses to vaccines against the variants” of Sars-CoV-2 “among healthcare professionals”. Finally, the data suggest that “infection control measures will have to continue into the post-vaccine era”.
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