The promise was good: in a single injection, the Janssen vaccine was to offer good protection against covid-19. As it happens, 66.9% reduced risk of having a moderate to severe form of the disease. This is what the subsidiary of the Johnson & Johnson group indicated after its phase 3 clinical trial, based on the original strain of SARS-CoV-2. But the arrival of the Delta variant has weakened this bet of the single dose …
2.6% of complete vaccinations in Brittany
After the green light from the health authorities, vaccination with the Janssen vaccine started in France on April 24, 2021, in people over 55 years of age. Much less used than its competitors, it has still been administered to a million French people but it has hardly been used since August. In Brittany, on September 9, only 2.6% of complete vaccinations had been carried out with this product, according to Public Health France, that is to say a total of 65,000 Bretons concerned.
But if these thousands of Bretons want to benefit from optimal protection against the Delta variant, they will have to go through the booster box with a very effective RNA vaccine, at least four weeks after their first injection. On August 24, the High Authority for Health justified it as follows: : “The available data do not confirm the long-term efficacy of the one-dose vaccination schedule of Janssen vaccine against the Delta variant”. In the process, the Directorate General of Health published an urgent note, placing the “Janssenized” French among the populations eligible for a vaccination booster from September 2021. In France, the first signs of too light protection appeared at the end of May, when the orientation council of the vaccine strategy already recommended to offer, in a territory affected by a cluster of Delta variant, a second dose of RNA vaccine to people who have received an injection of Janssen vaccine.
Vaccinated patients in intensive care
On Monday, the drug safety agency, ANSM, came to provide new information : two regional pharmacovigilance centers observed an over-representation of patients vaccinated with Janssen among patients vaccinated and hospitalized for covid-19 in intensive care: four out of seven in Marseille, three out of six in Tours. In addition, 32 cases of infection were observed following vaccination with this product, including four deaths from covid-19. “The people concerned have a median age of 68 years, with multiple risk comorbidities of serious form”, detailed the ANSM which now considers that it is a “potential signal” and wishes “to continue its investigations “. In Brittany, only one vaccine failure with Janssen was recorded by the regional pharmacovigilance center of Brest. It was about a person suffering from non-serious symptoms: an influenza-like illness with difficulty in breathing. No case has been traced back to that of Rennes.
Double injection “more relevant, in theory”
This loss of performance from the single dose does not surprise scientists: “As an immunologist, we prefer to stimulate the immune system in two stages: an initial injection then a boost for maximum efficiency. From a theoretical point of view, this seems more relevant: the first makes it possible to select the right white blood cells which will produce the antibodies suitable for the vaccine. On the second injection, these white blood cells kept in memory will become fully active, proliferate and produce large quantities of antibodies very quickly, ”explains Sandrine Sarrazin, researcher at the Marseille-Luminy immunology center (CNRS / Inserm / Aix-Marseille University). She underlines, moreover, that benefiting from injections of two different vaccines “is not at all annoying”. “On the contrary, this heterologous vaccination can provide cross-efficacy and increase the antibody portfolio,” she supports. Side effects side, the Marseille immunologist emphasizes that they are specific to each injection: “There is no memory effect of the first which would appear in the second”. In other words, a patient having benefited from a first injection of Janssen, and who would have just received another of RNA, will suffer only the possible side effects of the latter.