COVID-19 AstraZeneca and Pfizer vaccines have been associated with thrombosis and thrombocytopenia syndrome and myocarditis, respectively. While attempts have been made to contextualise adverse events following immunisation against the risks from COVID-19, this is complicated by constant changes in the pandemic landscape and accompanying updates in evidence informing the discussion. These changes include the emergence of new viral variants, associated reductions in vaccine effectiveness, waning vaccine effectiveness over time, case fatality rates, and local changes in public health measures regarding lockdowns and borders that influence COVID-19 community transmission levels.
To address the challenge of weighing up risks versus benefits of COVID-19 vaccines we developed a Bayesian network (BN) informed by Australian and international data, that calculates probabilities of outcomes under different scenarios of vaccine type and coverage, sex, age, community transmission intensity, variant, and vaccine effectiveness. This BN has been used to program the COVID-19 Risk Calculator (CoRiCal) (https://corical.immunisationcoalition.org.au), a user-friendly online tool that enables scenario analysis based on user inputs of age, sex, vaccination status, and transmission scenario. The tool can be used by health managers and individuals alone or in conjunction with clinicians for shared decision making on vaccination.
The model is easily updated to include emerging best evidence, data pertinent to different countries or vaccines, and outcomes such as long COVID. Moving beyond the pandemic, the model can function as proof-of-concept for the use of BNs as risk-benefit analysis tools in other healthcare contexts to prevent, prepare for and manage vaccine-preventable diseases into the future.