Table 1. Reported VITT incidence in COVID-19 vaccination.
| Analysis of pharmacovigilance reporting results | |||||
| Vaccine | Country (study population) | VITT cases | Incidence* | Key findings | Ref. |
| ChAdOx1 nCov-19 | Europe EudraVigilance (34,000,000) | 222 (VTE: 222) | 1/153,153 | Incidence lower than estimated rates for the general population, but unusual thromboses were listed as a rare side effect of the ChAdOx1 nCov-19 vaccine. | 10 |
| ChAdOx1 nCov-19 | Germany (2,700,767) | 31 (VTE: 31) | 1/87,121 | Germany suspended the ChAdOx1 nCov-19 vaccine for regular use in persons under 60. | 15 |
| ChAdOx1 nCov-19 | United Kingdom (21,200,000) | 77 (VTE: 77) | 1/275,325 | Thrombotic risk after vaccination lower than that observed for hospitalized COVID-19 patients. | 16 |
| Ad26.COV2.S | United States (7,200,000) | 12 (VTE: 12) | 1/600,000 | A warning on rare clotting events was added to the Ad26.COV2.S vaccine. | 17 |
| BNT162b2 | Europe EudraVigilance (54,000,000) | 35 (VTE: 35) | 1/1,542,857 | Currently undergoing safety review by the EMA. | 1 |
| BNT162b2 | United States VAERS (18,841,309) | 15 | 1/1,256,087# | Observed case numbers are not greater than those expected for the general population. | 18 |
| mRNA-1273 | Europe EudraVigilance (4,000,000) | 5† (VTE: 5) | 1/800,000 | Currently undergoing safety review by the EMA. | 1 |
| mRNA-1273 | United States VAERS (16,260,102) | 13 | 1/1,250,777# | Observed case numbers are not greater than those expected for the general population. | 18 |
| BNT162b2mRNA-1273 | United States (20,000,000) | 20 (VTE: 20) | 1/1,000,000 | Incidence may be comparable or lower than coincidental rates, but asymptomatic and mild cases may be underreported. | 19 |
| ChAdOx1 nCov-19, BNT162b2, mRNA-1273 | Global WHO Vigibase (361,734,967) | 2,169 (VTE: 795; ATE: 1,374) | 1/166,775 | ATE and VTE were comparable for the ChAdOx1 nCov-19 vaccine, but 2-3 times more ATE than VTE were reported for the mRNA vaccines. | 8 |
| Retrospective analysis of vaccinated populations | |||||
| Vaccine | Country (study population; female percentage) | VITT cases | Incidence* | Key findings | Ref. |
| ChAdOx1 nCov-19 | Denmark (148,792; 80%), Norway (132,472; 78%) | 142 (VTE: 59; ATE: 83) | 1/1,981 | Increased rates of VTE were observed following vaccination, and Denmark and Norway have since suspended use of the ChAdOx1 nCov-19 vaccine. | 20 |
| ChAdOx1 nCov-19 | Nepal (5,591; N/A) | 1 | 1/5,591 | Potential deep vein thrombosis was observed in a serious case. | 21 |
| ChAdOx1 nCov-19 | South Korea (5,589; 77%) | 0 | 0 | No VITT cases were noted. | 22 |
| BNT162b2 | South Korea (277; 77%) | 0 | 0 | No VITT cases were noted. | 22 |
| BNT162b2mRNA-1273 | United States (489,871; 59.1%) | 24 | 1/20,411 | Thrombosis rates remain lower than that in COVID-19 patients. | 23‡ |
| Prospective large-scale post-marketing phase IIIb or phase IV studies | |||||
| Vaccine | Country (study population) | VITT cases | Incidence* | Key findings | Ref. |
| ChAdOx1 nCov-19 | Scotland (1,707,962) | 4,319 (VTE: 893; ATE: 3,288) | 1/395 | An association was found between ChAdOx1 nCov-19 vaccination and higher risk of ITP and ATE. | 24 |
| Ad26.COV2.S | South Africa (288,368) | 0 | 0 | Five thrombotic events were reported in subjects with known thromboembolism risk factors, but no VITT cases were noted. | 25 |
| BNT162b2 | Scotland (821,052) | 2,084 (VTE: 421; ATE: 1,603) | 1/394 | No associations with ITP, VTE, or ATE were noted for BNT162b2 vaccination. | 24 |
* Incidence is presented as VITT events per vaccinated people, except # reflects VITT events per vaccination doses. † Unvetted numbers at time of publication. ‡ The data in this reference was cited from a pre-print study by Taquet M et al. Cerebral venous thrombosis: a retrospective cohort study of 513,284 confirmed COVID-19 cases and a comparison with 489,871 people receiving a COVID-19 mRNA vaccine. Available from: URL: https://osf.io/a9jdq/.
ATE, arterial thrombotic events; EMA, European Medicines Agency; ITP, idiopathic thrombocytopenic purpura; N/A, not available; Ref., reference number; VAERS, Vaccine Adverse Event Reporting System; VITT, vaccine-induced immune thrombotic thrombocytopenia; VTE, venous thrombotic events; WHO, World Health Organization.