The cases of acute myocarditis that occurred after the administration of the anti-Covid vaccine to mRna appear to be “extremely rare in the adult population aged 18 and over“. This is what emerges from a cohort study conducted in the US and based on a population of almost 2.4 million people who received at least one dose. On the analyzed cohort – made up of over 18s, from the Kaiser Permanente network of medical centers Southern California (Kpsc) – the incidence of these rare events was 5.8 cases per 1 million people after the second dose (1 case per 172,414 fully vaccinated subjects).
“The signal of increased myocarditis in young people deserves further investigation“, however, write the researchers Anthony Simone and colleagues, in the Research Letter published in these days in the journal ‘Jama Internal Medicine’.
“We evaluated acute myocarditis incidence and clinical outcomes among adults after mRna vaccination in an integrated health care system operating in the United States,” explain the researchers. The people studied were vaccinated between December 14, 2020 and July 20, 2021. Potential cases of post-vaccine myocarditis were identified based on physicians’ reports to a committee on immunization practices and hospitalizations within 10 days of administration of the vaccine with a diagnosis of myocarditis at discharge. All cases were independently judged by at least two cardiologists.
The incidence data obtained on this cohort were compared with those of people not exposed to the Covid vaccine. Of the 2.4 million subjects with at least one active dose of vaccine examined, half had received Moderna and half Pfizer / BioNTech. In this cohort, 54.0% were female, 31.2% were white, 6.7% were black, 37.8% were Hispanic, and 14.3% were Asian. Average age: 49 years, with 35.7% under 40 and 93.5% vaccinated with full cycle.
In the vaccinated group there were 15 cases of confirmed myocarditis (two after the first dose and 13 after the second), for an observed incidence of 0.8 cases per 1 million first doses and 5.8 cases per 1 million second doses in a 10 day observation window. All the patients in question were men, with an average age of 25 years, also in line with what emerged from other studies. In the unexposed group, there were 75 cases of myocarditis during the study period, of which 39 (52%) were men, mean age 52 years.
Of the post-vaccination myocarditis patients, none had prior heart disease. Eight patients received Pfizer and 7 Moderna. All were hospitalized and tested negative for SARS-CoV-2. 93% reported chest pain 1 to 5 days after vaccination. Symptoms resolved in all cases and no patients required ICU admission or returned to hospital after discharge. Given the observational nature of the study, no relationship between Covid mRna vaccination and post-vaccination myocarditis has been established.