In a European context of deployment of vaccination campaign against Covid-19, several countries want to speed it up, especially for the most fragile people. One of the solutions adopted, particularly in the United Kingdom and Denmark, is to postpone the second injection of the vaccine, for example in the context of the Pfizer-BioNTech vaccine, the administration of which is based on two doses spaced at least 21 days apart. The goal: to allow health authorities to have more doses available and thus extend vaccination coverage to more patients faced with the need to vaccinate as many as possible as quickly as possible.
But this measure would not be without risk, as stated by the Academy of Medicine in a recent review. Of course, the organization believes that it is important to compensate for the low availability of vaccine stocks, main limiting factor carrying out a mass vaccination. The latter also recalls that two agencies, the World Health Organization and the European Medicines Agency, have accepted that the 21-day delay between the administration of the two doses of the Comirnaty vaccine (Pfizer-BioNTech) be delayed for a few weeks. In France, the ANSM * has also declared itself in favor of the extension of this period to 42 daysin a notice published on January 07.
The risk: low immunity in the population
But on the other hand, the BioNTech laboratory itself was keen to let it be known that the vaccine efficacy rate is only 52% after the first dose: it amounts to only 95% when the second dose has been given to 21 days. It “does not guarantee such a high efficiency rate if the second injection is postponed beyond”, notes the Academy of Medicine. However, the United Kingdom, faced with a major resurgence of the epidemic linked to the spread of a highly transmissible variant for several weeks, has for example chosen a period of 12 weeks between the two injections in order to be able to double the number of people vaccinated for the first time in the next three months.
But what are the potential risks induced by this enlargement? “In the current context of epidemic upsurge, it is persistence of low immunityor even insufficient, during the extra weeksbefore the second injection which must be taken into consideration, ”explains the Academy. From an individual point of view, it evokes a specific risk, that of “aggravation by facilitating antibodies”. Either when the infection occurs in a person having low antibody levels neutralizers against the virus: postponing the second injection prolongs this state of increased receptivity. This method would also present its limits from a collective point of view.
Continue to apply barrier gestures
The Academy says in fact that it fears that “obtaining an expanded vaccination coverage, but weakened by a low level of immunity “Does not constitute favorable ground” forselect theemergence of one or more variants escaping immunity induced by vaccination. “Its experts nevertheless concede that” the late administration of a booster injection does not compromise its effectiveness since it is generally followed by a rapid re-rise of antibodies and a lasting strengthening of protective immunity. »Faced with the advantages and disadvantages of this practice, the organization recommends complying as much as possible with the prescribed vaccination schedule by the manufacturer.
For the Pfizer / BioNTech vaccine, the injection of the second dose must therefore be done 21 days later, compared to 28 days later. for the Moderna vaccine approved by the European Medicines Agency (EMA) on January 6. If circumstances so require (lack of available doses) the injection of the second dose may be postponed but not exceeding 3 weeks. Above all, the Academy recommends to “reserve this enlargementpeople under 50 and not presenting any risk factor of severe form of Covid-19 “and” to assess the impact of this enlargement on the increase in the number of people first-vaccinated each week. ”
Finally, the Academy of Medicine insists on the fact than barrier measures should be maintained so that anyone vaccinated can avoid infection before the second dose is given. Same recommendation for Health Insurance which specifies that “the available vaccines reduce the severity of symptoms but not contagiousness. You must therefore continue to isolate yourself in the event of a positive Covid-19 test, contact with a positive person or symptoms. The barrier gestures must always be applied scrupulously. The mask remains recommended, including for vaccinated people. It should be noted that since the start of vaccination in France, 189,834 people have been vaccinated according to the Ministry of Health.
To find out more about the coronavirus, the editorial staff invites you to discover its more complete and regularly updated articles:
- an article on Covid-19 disease and the evolution of the epidemic
- an article on the different screening tests
- an article on vaccines under development.