Recently released Nationwide cohort study in Denmark. Overall, more than 2.2 million triple-vaccinated individuals were included in the cohort; their average age was 66.9 years, and most individuals (52%) were females. Among these, over 1.7 million (78.2%) subjects were boosted with the bivalent vaccine between September 15 and December 10, 2022.
Bivalent mRNA boosters targeting the ancestral SARS-CoV-2 and the Omicron BA.1 or BA.4/5 spikes were approved for use in 2022. These bivalent boosters were recommended following primary vaccination (two-dose regimen).
Danish residents aged 50 or older were eligible if they received three doses of monovalent COVID-19 vaccines. Individuals were excluded if their third or fourth vaccine dose was administered within 90 days after the last dose. The primary risk period was 28 days post-bivalent vaccination and the reference period began on day 29 after the third/fourth dose.
Results: 1,740,417 individuals (mean age 67.8 years, standard deviation 10.7) received a bivalent omicron-containing mRNA-booster vaccine as a fourth dose. Nine myocarditis and 22 pericarditis cases were observed within 28 days after bivalent vaccination. Fourth dose vaccination with a bivalent omicron-containing booster did not statistically significantly increase the rate of any of the 27 adverse outcomes within 28 days, nor when analyzed according to age, sex, vaccine type, or using alternative analytical approaches. However, post-hoc analysis detected signals for myocarditis (statistically significantly so in females), although the outcome was very rare and findings were based on few cases. No risk of cerebrovascular infarction was found.
Bivalent mRNA boosters targeting the ancestral SARS-CoV-2 and the Omicron BA.1 or BA.4/5 spikes were approved for use in 2022. These bivalent boosters were recommended following primary vaccination (two-dose regimen).
Danish residents aged 50 or older were eligible if they received three doses of monovalent COVID-19 vaccines. Individuals were excluded if their third or fourth vaccine dose was administered within 90 days after the last dose. The primary risk period was 28 days post-bivalent vaccination and the reference period began on day 29 after the third/fourth dose.
Results: 1,740,417 individuals (mean age 67.8 years, standard deviation 10.7) received a bivalent omicron-containing mRNA-booster vaccine as a fourth dose. Nine myocarditis and 22 pericarditis cases were observed within 28 days after bivalent vaccination. Fourth dose vaccination with a bivalent omicron-containing booster did not statistically significantly increase the rate of any of the 27 adverse outcomes within 28 days, nor when analyzed according to age, sex, vaccine type, or using alternative analytical approaches. However, post-hoc analysis detected signals for myocarditis (statistically significantly so in females), although the outcome was very rare and findings were based on few cases. No risk of cerebrovascular infarction was found.
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