• Last updated: Sat, Apr 27, 2024Status: Ongoing
• Adam Altmejd, Dominik Dietler, Tove Fall, Torsten Persson, and Olof Östergren

Vaccine effectiveness identified from age cutoffs

The purpose of this project is to estimate how effectively COVID-19 vaccines prevent severe illness and death. Effectiveness, measured from real-world data, can differ from the efficacy numbers produced by clinical trials for several reasons. Mainly, people change their behavior once they are vaccinated, perhaps taking more risks of infecting themselves or passing on an infection onto others. The general population may also differ from trial participants in terms of age, comorbidities and simultaneous use of other pharmaceuticals that may moderate the effects of the vaccine.

To estimate the real-world effectiveness we will take advantage of the fact that vaccines were rolled out in Sweden using staggered year-of-birth cutoffs. For example, at a certain date, in a certain region, everyone born, in 1965 or earlier were allowed to get vaccinated, but not those born later. Two weeks later, vaccinations opened for those born 1970 or earlier. Since the exact date of birth of an individual is basically random, people born just below or above the age cutoffs form comparable groups that only differ in terms of access to the vaccination. The staggered rollout of the vaccines thus constituted a set of natural experiments, each of which consists of well-defined treatment groups and control groups of individuals with the same characteristics. We will use this quasi-random variation in a regression discontinuity design to estimate vaccine effectiveness.