Meta-Analysis of Risk of Vaccine-Induced Immune Thrombotic Thrombocytopenia Following ChAdOx1-S Recombinant Vaccine

Abstract

Context

Vaccine-induced immune thrombotic thrombocytopenia (VITT) has been reported after administering ChAdOx1-S recombinant COVID-19 vaccine (marketed as Vaxzevira™ by Astra-Zeneca, Covishield™). Estimates of incidence vary between countries, due to different age distributions chosen, case definitions and choice of denominator (persons vaccinated vs immunizations given). This study clarifies these estimates by pooling data from ten countries and examining differences by age group.

Methods

We examined case reports, press releases and immunization data and calculated pooled estimates of VITT incidence using random effects models. Sensitivity analyses considered different combinations of countries and varying assumptions on time between vaccination and reporting of cases.

Results

Pooling all countries, VITT incidence was 0.73 per 100,000 persons receiving first dose of Covishield/Vaxzevira [95% CI .43,1.23]. Incidence for age 65 and over was 0.11 per 100,000 persons [95% CI .05-.26], and significantly higher among those under age 55: 1.67 per 100,000 persons [95% CI 1.30-2.14] in the UK, 5.06 per 100,000 persons in Norway [95% CI 2.16, 11.86]. The latter had the best data on counts of persons vaccinated. Incidence for age 55 to 64 years was 0.34 [95% CI 0.13, 0.85] in the UK, lower than for under age 55.

Conclusion

VITT is a rare vaccine-associated adverse event. Incidence estimates vary between jurisdictions. However, even the highest reported incidence from Norway is low – and in settings with high community transmission, lower than risk of serious outcomes associated with Covid-19. Policymakers and individuals can use these data to calculate risk-benefit ratios and better target vaccine distribution.

Essentials

This paper measures risk of vaccine-induced immune thrombotic thrombocytopenia (VITT) after ChAdOx1-S recombinant COVID-19 vaccine
Pooled estimates of incidence were calculated with a random effects model based on data from 10 countries
Overall risk is 1 in 139,000; for age 65 and over, about 1 in 1,000,000; for age under 55, between 1 in 20,000 to 60,000
VITT risk is low and varies by age. These data can inform policies around vaccination distribution.

SciScore for 10.1101/2021.05.04.21256613: (What is this?)

Please note, not all rigor criteria are appropriate for all manuscripts.

Table 1: Rigor

Ethics	not detected.
Sex as a biological variable	not detected.
Randomization	These policy differences arose from fact that Covishield/Vaxzevira initially had only limited efficacy data from randomized trials on the 65 and over population, which led to some but not all countries restricting its use to those under 65.
Blinding	not detected.
Power Analysis	not detected.

Table 2: Resources

Software and Algorithms
Sentences	Resources
These policy differences arose from fact that Covishield/Vaxzevira initially had only limited efficacy data from randomized trials on the 65 and over population, which led to some but not all countries restricting its use to those under 65.	Covishield/Vaxzevira suggested: None

Results …

SciScore for 10.1101/2021.05.04.21256613: (What is this?)

Please note, not all rigor criteria are appropriate for all manuscripts.

Table 1: Rigor

Ethics	not detected.
Sex as a biological variable	not detected.
Randomization	These policy differences arose from fact that Covishield/Vaxzevira initially had only limited efficacy data from randomized trials on the 65 and over population, which led to some but not all countries restricting its use to those under 65.
Blinding	not detected.
Power Analysis	not detected.

Table 2: Resources

Software and Algorithms
Sentences	Resources
These policy differences arose from fact that Covishield/Vaxzevira initially had only limited efficacy data from randomized trials on the 65 and over population, which led to some but not all countries restricting its use to those under 65.	Covishield/Vaxzevira suggested: None

Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

Results from LimitationRecognizer: An explicit section about the limitations of the techniques employed in this study was not found. We encourage authors to address study limitations.

Results from TrialIdentifier: No clinical trial numbers were referenced.

Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

Results from JetFighter: We did not find any issues relating to colormaps.

Results from rtransparent:

Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
No protocol registration statement was detected.

Results from scite Reference Check: We found no unreliable references.

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