Monkeypox: How much protection can we expect from a single dose of vaccine?


Although data published in scientific journals do not really allow us to estimate the durability of protection against monkeypox, the results of a clinical trial presented in 2019 suggest that it could be long-lasting. using a third-generation smallpox vaccine (1), it was one dose if previously vaccinated against smallpox in the past, two doses four weeks apart otherwise, with a third injection recommended for the immunocompromised. The level of protection against infection or severe forms has not yet been accurately assessed. In a context of a health emergency, and due to the low availability of licensed vaccines to combat monkeypox, the Ministry of Health indicated that the 28-day period “would be extended for non-immunosuppressed people.” In recent days, several witnesses have reported cancellations of appointments for their second dose in France. In this situation, which is not unique to France, several public health actors question the effectiveness of injecting a single, single dose of the famous vaccine in people who have never been vaccinated… Few solid elements in the scientific literature What do scientific studies published in peer-reviewed journals say about this question? For now: not much. Only studies in mice, conducted in the early 2000s, have analyzed the type of immune reaction induced by a single dose of vaccine, suggesting the interest of one or more additional doses to prolong the benefits. In fact, most subsequent trials evaluate the performance of double injections. In 2013 and 2017, studies tested different regimens in which the second injection is given without waiting four weeks, resulting in a weaker immune reaction. Although these observations confirm the interest of a schedule of two doses separated by at least months, they do not therefore answer a question of general interest: how quickly the defenses acquired in the case of a single and single injection of this vaccine? of the studies that assess the immune response always include a second injection, and the few that study the effects of a single dose… don’t do long-term measurements. In a study on macaques published in 2008, protection against the virus responsible for monkeypox was observed within four to six days after injection. It is not known, however, how long this protection can be maintained. Bernard Moss, co-author of the 2008 paper, confirms to CheckNews that “the goal of the study was to determine how quickly immunity was achieved with a dose. We did not attempt to determine the duration of protection.” At least two years of protection, according to the results published online in 2019. In the absence of properly peer-reviewed and peer-reviewed studies, we have to resort – with all reservations – to the results of clinical trials that have not yet been submitted to scientific journals . In a recent exchange with a Science reporter, researcher Paul Chaplin, also CEO of the company that produces the vaccine, referred to “studies showing that immune responses elicited by a single injection declined after two years.” “The immune memory is so strong after a single dose, he told the scientific journal, that a booster administered two years later elicits the same immune response as the standard program. When asked by CheckNews, Paul Chaplin clarified that he was referring to a clinical trial completed in 2009, the results of which were published online in 2019. The trial evaluated antibody levels in the blood of about 300 volunteers who participated in a previous vaccine study. Among them, 183 people who had never been vaccinated against smallpox had received one or two doses of the vaccine. According to publicly available data, significantly elevated antibody levels can still be detected two years after a single injection. Likewise, administration of a second dose after this time appears to complete the vaccination schedule satisfactorily. Studied in the context of an epidemic” and found it difficult to extrapolate information from data on immune responses presented in animal studies available to date. (1) Manufactured. of Bavarian Nordic and marketed under different names in different countries (Imnavex, Jynneos, etc.), is a non-replicative live attenuated vaccine (a virus unable to reproduce in cells), originally developed against smallpox. Each vial contains a standard dose of the vaccine. Unless otherwise noted, the publications we cite refer to standard-dose vaccine injections, comprising between 50 and 395 million infectious units.
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