Continuing COVID-19 Vaccination of Front-Line Workers in BC with the AstraZeneca Vaccine: Benefits in the Face of Increased Risk for Prothrombotic Thrombocytopenia

Accompanying analysis and reproducible R Markdown manscript for Continuing COVID-19 Vaccination of Front-Line Workers in BC with the AstraZeneca Vaccine: Benefits in the Face of Increased Risk for Prothrombotic Thrombocytopenia (Adibi et al. 2021). The preprint is on medRxiv: https://www.medrxiv.org/content/10.1101/2021.04.11.21255138v1

The compartmental model used here is based on Mulberry et al., 2021.

Abstract

Background: In March 2021, a number of regulatory and advisory bodies around the world recommended against using the AstraZeneca COVID-19 vaccine in younger adults pending further review of the risk for vaccine-induced prothrombotic immune thrombocytopenia (VIPIT). As an example, we consider the Canadian province of British Columbia (BC) which halted its front-line workers vaccination program with the AstraZeneca vaccine. The province received an additional 246,700 doses of AstraZeneca vaccine in the weeks before April 11th, enough to provide the first dose of vaccine to all unvaccinated front-line workers. It is unclear whether the alternative, mRNA vaccines can be immediately made available to front-line workers.

Methods: We reviewed the latest available evidence and used compartmental modelling to 1) compare the expected number of deaths due to COVID-19 and VIPIT under the scenarios of immediately continuing vaccination of front-line workers with the AstraZeneca vaccine or delaying it in favour of mRNA vaccines from a societal perspective, and 2) compare the individual mortality risk of immediately receiving the AstraZeneca vaccine with waiting to receive an mRNA vaccine later from a personal perspective.

Results: We estimate that if British Columbia continues the front-line worker vaccination program with the AstraZeneca vaccine, we expect to see approximately 45,000 fewer cases of COVID-19, 800 fewer hospitalizations, 120 fewer COVID-related deaths, and 2,300 fewer cases of Long COVID from April 15th to October 1st, 2021, for an expected number of VIPIT-related deaths of 0.674 [95% CI 0.414-0.997]. In the same period and in areas of high transmission ($R_0$=1.30), the projected excess risk of mortality due to COVID-19 and VIPIT was significantly higher in the delayed vaccination with mRNA vaccines scenario (3.5 to 4.5 times higher risk) than that of immediate vaccination with the AstraZeneca vaccine for those between 30 and 69 years of age. In areas with lower levels of transmission ($R_0$=1.15), the projected excess risk of mortality was 1.8 to 3.4 times higher in the delayed vaccination with mRNA vaccines scenario for those between 30 and 69 years of age. For those under 30, immediate vaccination with the AstraZeneca vaccine posed a higher risk than delayed vaccination with an mRNA vaccine, regardless of the level of transmission in the community.

Conclusions: The benefits of continuing immunization of front-line workers with the AstraZeneca vaccine far outweigh the risk both at a societal level and at a personal risk level for those over 40, and those over 30 in high-risk areas.

keywords: COVID19; vaccination; front-line workers; blood clots; vaccine-induced prothrombotic immune thrombocytopenia; harm-benefit; BC