Systematic Review Finds Higher Risk of Thromboembolic Events Following First Dose of ChAdOx1-S Vaccine

To determine the same, a systematic review and meta-analysis of analytical studies were conducted by Raman S Vaman, Scholar, ICMR-School of Public Health, ICMR- National Institute of Epidemiology, Chennai, Tamil Nadu, India and colleagues.

Two independent reviewers screened for eligible studies, extracted data, and assessed the risk of bias. The DerSimonian-Laird random effects model was used to pool the incidence rate ratios (IRRs) separately for the first and second doses. Heterogeneity was measured using I2 statistics. A total of 20 studies were included, comprising 11 self-controlled case series and nine cohort studies, with a combined participant pool of 254 million.

Research indicated the following findings:

• A meta-analysis of 17 studies revealed an elevated risk of cerebrovascular thrombosis (IRR = 3.5), portal vein thrombosis (PVT) (IRR = 2.0), and thrombocytopenia (IRR = 1.6) in individuals who received the ChAdOx1-S vaccine compared to controls.
• No increased risk was observed after the second dose or for secondary outcomes.

“Since most studies were conducted in Europe, it is crucial to develop national-level databases in low- and middle-income countries to monitor rare adverse events in the post-marketing phase,” researchers concluded.

Reference: Vaman, Raman S.^*; Kumar, Muthusamy S.^1,*; Jeyashree, Kathiresan²; Periasami, Ashok; Abdulkader, Rizwan S.³; Murhekar, Manoj⁴. Association between COVID-19 Vaccination (ChAdOx1-S) and Thromboembolic, Thrombocytopenic, Hemorrhagic Events: A Systematic Review and Meta-analysis of Analytical Epidemiological Studies. Indian Journal of Community Medicine 49(4):p 571-578, Jul–Aug 2024. | DOI: 10.4103/ijcm.ijcm_676_23.