Compare Immunological Efficacy of a Vaccine Regimen Combining Two Covid19 mRNA Vaccines (Pfizer-BioNTech and Moderna) With That of a Homologous Vaccination of Each Covid19 mRNA Vaccine

As part of the COVID 19 vaccine campaign, the two mRNA vaccines, BNT162b2 (COMIRNATY®) and mRNA-1273 COVID-19 vaccine Moderna, are administered in two doses in subjects without a history of SARS-CoV-2 infection . In accordance with the marketing authorization for vaccines, HAS recommends that subjects who have received one dose of an mRNA vaccine receive a second dose of the same vaccine with an interval between the 2 doses of 4 to 6 weeks. These two vaccines are based on very similar technologies but were developed independently. Given the similarities between these two vaccines, the choice between the two, for the moment, is based solely on the availability of doses and on logistical constraints. Since April 14, the interval between the two doses of the mRNA vaccines is 42 days. WHO has announced that in the absence of available data, vaccine interchangeability cannot be recommended. However, to facilitate the organization of the vaccination campaign and allow faster vaccination of the population, it would be desirable to be able to use either one or the other mRNA vaccine for the 2nd dose. In order to be able to recommend the interchangeability of the 2 mRNA vaccines, it is proposed to evaluate the immunogenicity of a scheme combining the two Covid 19 mRNA vaccines (i.e. a 2nd dose of vaccine with the Moderna vaccine after a first dose of the Pfizer vaccine or 2nd dose of Pfizer vaccine after a first dose of Moderna vaccine) compared to that of a standard vaccination schedule with two doses of the same Covid 19 mRNA vaccine.