Vaccines have been shown to be extremely effective in protecting those who have never had Covid, but their effectiveness in preventing symptoms and serious outcomes in people who have been infected in the past has, until recently, been less clear. Now two separate pieces of research, published in the journal Lancet Infectious Diseases, confirm that Covid-19 vaccines provide additional protection for people already infected with Sars-CoV-2 – especially against severe disease. In the first study, conducted in Brazil, researchers found that four vaccines – CoronaVac, Oxford / AstraZeneca, Janssen and Pfizer / BioNTech – provide additional protection against accidental re-infection and serious outcomes, such as . The second study, from Sweden, found that the Covid-19 vaccine provided additional protection to those who had previously had Covid for at least nine months. Together, the studies provide critical data on the effectiveness of the vaccine in people with a previous infection and highlight the benefits of the vaccine regardless of whether anyone has had Covid. Experts say the findings could also help update global vaccine strategies. “Covid-19 vaccines have been shown to be extremely effective in preventing symptomatic infection and hospitalization in people without a previous infection, but the effectiveness for those with a previous infection is less clear,” said Julio Croda, author of the first study at Universidade Federal. de Mato Grosso do Sul and Fundação. “Understanding the duration and effectiveness of immunity for those vaccinated with a previous diagnosis of Covid-19 is becoming increasingly important as the pandemic progresses and erupts; new cases may occur as a result of more contagious variants. “Further research on the need for vaccination for those who have a previous Covid-19 infection is a vital step in pandemic policy intervention, including guidance on single- or two-dose vaccine protection.” In the first study, which involved more than 22,000 people re-infected with Covid, the data showed that vaccination reduced the risk of symptoms, hospitalization or death. “All four of these vaccines have been shown to provide significant additional protection to those with a previous Covid-19 infection, reducing hospitalization and death,” Croda said. “There is an ongoing public debate about whether people who have been infected in the past should be vaccinated. “Our results suggest that the benefits of the vaccine far outweigh any potential risks and support the case for vaccination, including the full range of vaccines, among people with a previous Sars-CoV-2 infection.” Writing in the same journal, Pramod Kumar Garg, of the Translational Health Science and Technology Institute in India, who did not participate in the study, said: [the Brazil] study and other recent studies challenge the notion of herd immunity in the population through natural infection only against Sars-CoV-2 and suggest that vaccinating previously infected individuals provides further protection, especially against severe disease. “These data should help guide policy decisions and alleviate vaccination hesitation among people who have had Sars-CoV-2 infection.” The second study, which involved nearly 3 million people, found that one dose of the vaccine in someone with an immunity due to a previous infection reduced their risk of re-infection by 58% two months after the vaccine. Two doses of the vaccine reduced the risk of infection by 66%. The authors identified limitations in both studies, including the risk of bias due to the observational nature of the research. In addition, no studies included re-infection analysis of Omicron variants. Writing in the same journal, Jennifer Juno, of the University of Melbourne, Australia, who did not participate in either study, said: recovered from Covid-19. “
