Factors associated with thrombotic events among young adults in India, 2021-23: A multi-centric hospital-based matched case -control study.

Background and objectives Myocardial infarction (acute coronary artery thrombotic event) in young adults is known to be associated with certain comorbidities and lifestyle factors. The causal relationship between COVID-19 vaccination and thrombotic events has been debated globally, with varying risks being reported across populations and vaccine platforms. Considering reports of myocardial infarction and other thrombotic events in apparently healthy individuals, this study was conducted to determine the association between COVID-19 vaccination, lifestyle, medical risk factors, and thrombotic events among young adults in India. Methods We conducted a multicentric matched case-control study across 25 tertiary hospitals in India between October 2021 and January 2023. Cases were 18-45-yr-old hospitalised patients with new arterial or venous thrombotic events. Hospitalised cases and controls were matched by admission date (±7 days). Data on exposure factors were obtained through hospital records and telephonic interviews. Conditional logistic regression was used to estimate matched odds ratios (mOR) with confounder adjustments guided by a directed acyclic graph. Results We analysed 432 cases (1293 controls) of acute myocardial infarction and 767 cases (2,144 controls) of any thrombotic event. Acute myocardial infarction was associated with previous history of any thrombotic event [Matched Odds Ratio (mOR) 60.0; 95% Confidence interval (CI): 11.4, 315.1], comorbidities [adjusted mOR (amOR) 4.6; 95% CI: 2.0-10.5], ever smoking (amOR 3.5; 95% CI: 2.3-5.3) and family history of thrombotic event (mOR 3.3; 95% CI: 1.7-6.5). Receiving two or more doses of any COVID-19 vaccine (amOR 0.8; 95% CI: 0.3-2.8) was not associated with acute myocardial infarction. Analyses showed an association of any thrombotic event with prior history of thrombotic event, comorbidities, ever smoking, prior COVID-19 hospitalisation and family history of thrombotic event. There was no association between any thrombotic event and two or more doses (amOR 1.0; 95% CI: 0.5-2.0) of any COVID-19 vaccination. Similar associations were seen when analysed separately for CovishieldTM and CovaxinTM. Interpretations and conclusions Among young Indian adults, thrombotic events were driven by traditional risk factors and prior severe COVID-19 illness. No increased risk of thrombotic events, including myocardial infarction, was identified with COVID-19 vaccination given the widespread SARS-CoV2 infection during the study period. We emphasise the importance of addressing modifiable cardiovascular risk factors and monitoring of young adults with comorbidities, prior thrombotic events or severe COVID-19.