Arrived on the French market in October 2022 to replace the previous monovalent mRNA vaccine against Covid, the bivalent mRNA vaccine Comirnaty (Pfizer-BioNTech) targets both the ancestral and omicron variants of SARS-CoV-2. Problem: In January 2023, the US CDC (Centers for Disease Control and Prevention) ont announcement that in the 21 days following the injection of the bivalent vaccine, a possible increased risk of ischemic stroke had been noted in people over 65 years of age.
epi-lighthouse had not previously not found increased risk of stroke, myocardial infarction or pulmonary embolism after injection of the monovalent mRNA vaccine in patients over 75 years of age. In order to verify whether this absence of excess risk was verified with the bivalent booster, the researchers followed all French people over the age of 50 vaccinated between October 6 and November 9, 2022, a period during which monovalent and bivalent vaccines were available to vaccinate the over-50s. During this period, 932,593 French people over the age of 50 received the bivalent vaccine, and 121,362 people received the monovalent.
For each day between October 6 and November 9, 2022, the researchers randomly associated one vaccinated with the monovalent and five vaccinated with the bivalent; 373,728 people who received the bivalent were included in the analysis, as well as 97,234 people who received the monovalent vaccine (median age: 72.6 years; 53.8% female). The two cohorts had comparable sociodemographic and health status characteristics.
The subjects were followed up to 21 days after vaccination, and the researchers estimated their risk of ischemic or hemorrhagic stroke, myocardial infarction and pulmonary embolism. At the end of this analysis, the researchers found no no increase in risk with the bivalent vaccine for each of the four events tested in the over 50s. Although this is not an analysis restricted to those over 65, the authors conclude that their data “reassure about the continued use of these vaccines”.