THURSDAY, Oct. 27, 2022 (HealthDay News) — The risk for thrombocytopenia is increased after receipt of the ChAdOx1-S vaccine compared with BNT162b2, according to a study published online Oct. 26 in The BMJ.

Xintong Li, from the University of Oxford in the United Kingdom, and colleagues quantified the comparative risk for thrombosis with thrombocytopenia syndrome or thromboembolic events associated with use of adenovirus-based versus mRNA-based COVID-19 vaccines using routinely collected health data. A total of 1,332,719 of 3,829,822 first-dose ChAdOx1-S recipients were matched to 2,124,339 of 2,149,679 BNT162b2 recipients from Germany and the United Kingdom, and 762,517 of 772,678 recipients of Ad26.COV2.S were matched to 2,851,976 of 7,606,693 individuals receiving BNT162b2 in Germany, Spain, and the United States. All 628,164 U.S. Ad26.COV2.S recipients were matched to 2,230,157 of 3,923,371 mRNA-1273 recipients.

The researchers identified 862 thrombocytopenia events in the matched first-dose ChAdOx1-S recipients from Germany and the United Kingdom and 520 events after the first BNT162b2 dose. An increased risk for thrombocytopenia was seen comparing ChAdOx1-S with a first dose of BNT162b2 (pooled calibrated incidence rate ratio, 1.33 [95 percent confidence interval, 1.18 to 1.50] and calibrated incidence rate difference, 1.18 [95 percent confidence interval, 0.57 to 1.8] per 1,000 person-years). In addition, for Ad26.CoV2.S versus BNT162b2, there was a pooled calibrated incidence rate ratio of 2.26 (95 percent confidence interval, 0.93 to 5.52) for venous thrombosis with thrombocytopenia syndrome.

“Although rare, the observed risks after adenovirus based vaccines should be considered when planning further immunization campaigns and future vaccine development,” the authors write.

Several authors disclosed financial ties to the pharmaceutical industry.

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