Background

In January 2023, the Centers for Disease Control and Prevention (CDC) Vaccine Safety Datalink (VSD) and the FDA alerted to a possible risk of ischemic stroke within 21 days of administration of the bivalent Comirnaty vaccine in persons aged 65 years and older.

Objective and Method

The objective of this study was to assess whether the risk of occurrence of these events differed after receiving the booster dose of bivalent Comirnaty vaccine compared with monovalent Comirnaty in persons aged 50 years or older. On each day from October 6 to November 9, 2022, each person who received the monovalent vaccine was matched with up to five of the total number of persons who received the bivalent vaccine on the same day.

Results

In total, between October 6 and November 9, 2022, 1,148,036 subjects aged 50 years and older had received a booster dose of either the monovalent Comirnaty vaccine or the bivalent Comirnaty. Following matching on the day of vaccine administration, 470,962 subjects were finally selected, of whom 97,234 (20.6%) received monovalent Comirnaty and 373,728 (79.4%) bivalent Cominarty. There was no increased risk of ischemic stroke (n = 148; weighted hazard ratio (wHR), 0.9; 95% CI, 0.6 – 1.3), hemorrhagic stroke (n = 57; wHR, 0.9; 95% CI, 0.5 – 1.6), myocardial infarction (n = 151; wHR, 0.9 ; 95% CI, 0.6 – 1.4), pulmonary embolism (n = 84; wHR, 0.8; 95% CI, 0.5 – 1.4), or all four events combined (n = 439; wHR, 0.9; 95% CI, 0.7 – 1.1) could not be demonstrated within 21 days of administration of the bivalent Comirnaty vaccine compared with that of the monovalent vaccine.

Conclusion

Our results provide reassurance for the continued use of this bivalent vaccine.