context
Since April 2021, cases of myocarditis and pericarditis have been reported following administration of Covid-19 messenger RNA (mRNA) vaccines. A large-scale risk assessment of each vaccine is needed to inform public decisions. In a previous study of all cases of myocarditis and pericarditis occurring in France in people aged 12 to 50 between May 15 and August 31, 2021, we highlighted increased risks of hospitalization for myocarditis or pericarditis within 7 days following administration of each of the two mRNA vaccines, BNT162b2 (Comirnaty®, Pfizer-BioNTech) and mRNA-1273 (Spikevax®, Moderna). The association was strongest in people aged 12 to 29 and following the second dose of the mRNA-1273 vaccine. The results also showed a generally favorable clinical course of cases in the very short term, given the short duration of hospitalization and the absence of deaths during the hospital stay among patients exposed to recent vaccination.
The new analysis we present here includes cases that occurred up to October 31, 2021.
The objectives of this updated analysis are to complete the study in order to better specify risk estimates among adolescents and young adults and to describe more precisely the severity of cases of myocarditis and pericarditis occurring following vaccination.
Methods
A matched case-control study was conducted using data from the National Health Data System (SNDS) linked to data from the national information systems on vaccination once morest COVID-19 (VAC-SI) and on HIV testing. screening for SARS-CoV-2 (SI-DEP).
We analyzed all confirmed cases of myocarditis and pericarditis in people aged 12 to 50 years hospitalized between May 12 and October 31, 2021. Each case was matched to the date of hospital admission on age, sex and area of residence to 10 randomly selected controls from the general population.
Using conditional logistic regression models, we estimated the odds ratios of hospitalization for myocarditis or pericarditis associated with the first and second doses of each vaccine in the previous 21 days, separately by sex and age.
Results
Between May 12 and October 31, 2021, 46 million doses of mRNA vaccines were administered to people aged 12 to 50 in France, and 21 and 2.9 million of them respectively received at least one dose. BNT162b2 and mRNA-1273 vaccines. A total of 1612 cases of myocarditis and 1613 of pericarditis occurring in vaccinated and unvaccinated individuals were matched to 16,120 and 16,130 controls, respectively.
The risk of myocarditis and pericarditis is increased during the first week following administration of both vaccines in both males and females. The risk of myocarditis is highest following the second dose of mRNA-1273, with odds ratios reaching 44, respectively [IC95%, 22-88] and 41 [12-140] among men and women aged 18 to 24. The estimated excess of myocarditis cases is highest in men between 18 and 24 years old, reaching 4.7 [3,8-5,8] cases per 100,000 second doses of BNT162b2 and 17 [13-23] cases per 100,000 second doses of mRNA-1273. These rates correspond to one case of myocarditis attributable to vaccination for the administration of 21,100 [17 400-26 000] second doses of BNT162b2 and 5,900 [4 400-8 000] second doses of mRNA-1273. An increased risk of pericarditis is also found within 7 days following the second dose of each vaccine in men and women aged 12 to 50.
The length of hospital stay of cases occurring following recent exposure to an mRNA vaccine (4 days on the median) is equivalent to that of unvaccinated. On the other hand, stay in resuscitation, ventilation, and death were less frequent in the event of hospitalization following exposure to an mRNA vaccine. In addition, infection with SARS-CoV-2 in the previous month is strongly associated with the occurrence of myocarditis (adjusted odds ratio: 9.0 [6,4–13]) or pericarditis (adjusted odds ratio: 4.0 [2,7–5,9]).
Conclusions
This study confirms and measures the magnitude of an increased risk of myocarditis and pericarditis in the week following vaccination once morest Covid-19 by mRNA vaccines, in particular the second dose of the mRNA-1273 vaccine, in men and women aged 12 to 50. Cases of myocarditis and pericarditis following vaccination do not appear to be more serious than those occurring outside of vaccination.
