Moderna is the first laboratory to have publicly welcomed, on Tuesday, the effectiveness of an update of its vaccine against the BA.4 and BA.5 subvariants of the Omicron strain of Covid-19. For the first time in the fight against the pandemic, the American company has developed a bivalent vaccine. A type of vaccine that must protect against both the original strain of the virus and against the Omicron mutation. This is a timely press release. Moderna announced Wednesday, June 22, that the latest modified version of its flagship Covid-19 vaccine has proven more effective than previous ones in protecting against the BA.4 and BA.5 sublayers of the Omicron variant of the coronavirus. In fact, preliminary human tests have demonstrated up to six times greater efficacy in combating Omicron than Moderna’s initial version of the vaccine. is increasingly dominant in the world. In France, the epidemic recovery is confirmed at a time when the drop in the number of hospital admissions of people infected with Covid-19 has stopped, notes the daily Liberation. A darker horizon which would be essentially due to the BA.4 and BA.5 strains of Omicron, in the process of imposing themselves in France. Because having been vaccinated two or three times and even having already been contaminated by the Omicron strain would not provide adequate protection against these two terrible new children of the virus, according to researchers at Harvard University Medical School. Faced with the threat of a summer and especially an autumn which could be marked by a great return of the epidemic, the Moderna cavalry therefore seems to have arrived in time. And not with just any product. The booster shot that the American laboratory recommends is a bivalent vaccine. “It’s when there are two antigens in the same vaccine”, explains Pierre Saliou, associate professor of Val-de-Grâce and specialist in vaccination issues. In this case, Moderna has modified its initial product so that it induces the production, by the immune system, of antibodies against the original strain of Sars-CoV-2 and against Omicron. There is nothing revolutionary in this process. Other bivalent or multivalent vaccines have already existed for years, starting with the one against influenza. “Generally, these are quadrivalent vaccines which therefore attack four different strains of influenza”, specifies Pierre Saliou. Some vaccine compounds can even protect against more than twenty mutations of the same disease, as is the case with some vaccines against pneumococci, which are bacterial infections. The Omicron turning point This type of vaccine is not limited to fights against different forms of the same virus: it can also contain antigens against several very different diseases. “This is, for example, the case of the one administered to infants to protect them from diphtheria, tetanus, whooping cough, poliomyelitis and Haemophilus Pneumoniae type b infections”, recalls Pierre Saliou. Until today, this type of vaccine had not yet been developed for Covid-19, despite an ever-increasing number of mutations in the virus. “It’s simply because the vaccines that protect against the Wuhan strain have so far been sufficient for the other mutations. This no longer seems to be the case with Omicron,” said Penny Ward, visiting professor of pharmaceutical medicine at King’s College. of London. The development by Moderna of a bivalent booster dose demonstrates that we are at a turning point in the evolution of the virus. The first generations of vaccines are beginning to show their limits. “The other laboratories must surely be doing the same work, it’s just that they communicate less than Moderna”, estimates Jonathan Stoye, virologist and research manager at the Francis Crick Institute in London. These multivalent vaccines are “a little more expensive to develop, and it is more complicated to keep them because you have to be careful that it remains stable and that the molecules do not mix”, summarizes Penny Ward. But then why not focus on the development of a vaccine specifically studied to fight against Omicron specifically? The problem comes from Sars-CoV-2 which has been able to be particularly unpredictable. “Its evolution is not linear and the mutations go in all directions”, underlines Jonathan Stoye. Nothing says that in the fall a new strain, closer to the Delta variant than to Omicron, will see the light of day. In which case a vaccine that protects against the original form of Covid-19 – which has already demonstrated its effectiveness against other strains – would be more suitable than one intended solely to protect against Omicron and its sub-variants. Pending precise scientific data Omicron is the first variant that seems to confirm what some scientists have been saying for a long time: Covid-19 will become a disease which, like the flu, will require regular updates of the vaccine system. bring to the surface the debate around a potential universal vaccine against all coronaviruses. “It is very different from multivalent vaccines in that it is a molecule capable of creating antibodies protecting against all forms, even future ones, of a virus”, explains Pierre Saliou. A miracle cure “still very far from being relevant with regard to Covid-19”, assures Penny Ward. The fault of “everything that we do not yet know about the action of the virus on the immune system”, specifies Jonathan Stoye. Proof that the quest for a universal vaccine is difficult to carry out: “We still haven’t found one for the flu even though we’ve been working on it for much longer”, notes Penny Ward. But it’s not because a laboratory releases its 2.0 vaccine that will necessarily have to be administered to everyone immediately. “Moderna’s announcement is good news, but there is still a lack of scientific data that would allow us – the scientific community – to better understand how this bivalent vaccine works,” says Christine Dahlke, vaccine specialist at the German Center for infectious disease research. One piece of data that is missing, for example, is that which would make it possible to compare “the level of protection against BA.4 and BA.5 of this vaccine with that available to people who have already been infected with Omicron”, underlines this expert. . Such information would allow, according to her, to know if it is not appropriate to reserve this recall to the elderly and to those who have a comorbidity. At least, initially.
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