Vaccine-associated blood clot death: a micromort thinking

The unfortunate post-vaccinated death of a 48 yr old woman last week has raised concerns about the safety of the AstraZeneca vaccine (Vaxzevria). Here, I offer my interpretation of the risk in terms of micromort, and then my analysis of risk and benefit of the vaccination program.

Quantifying risk in micromort

The micromort concept was advanced by Ronald A. Howard in the 1980s for decision making. Basically, micromort (micro-mortality) is a way of representing probability of mortality for small and acute risks. Howard defined that a micromort is one-in-a-million chance of dying. So, if an activity that is associated with a probability of 10 deaths per 1 million, then the activity has 10 micromorts. Similarly, a 1% risk of death is equivalent to 10,000 micromorts. Micromort is a useful way to understand and convey microrisk associated with daily activities.

We now apply the idea of micromort to quantify the risk of death from blood clot associated with AstraZeneca vaccine (Vaxzevria). According to the European Medicine Agency (EMA), until 22/3/2021, 25 million people had received Vaxzevria; among whom, 18 had died from blood clot [1]. Thus, micromort for blood clot associated with Vaxzevria is 18 / 25 = 0.72.