In cooperation with colleagues from the Wittgenstein Centre for Global Human Capital Sanchez-Romero investigated the impact of COVID-19 vaccines on the Case Fatality Rate (CFR) with specific focus on the monitoring of break-through infections.
The study aimed to test the behavior of the CFR in a mixed population of vaccinated and unvaccinated individuals by illustrating the role of both the effectiveness of vaccines in preventing deaths and the detection of infections among both the vaccinated (breakthrough infections) and unvaccinated individuals. The authors simulated three hypothetical CFR scenarios that resulted from a different combination of vaccine effectiveness in preventing deaths and the efforts in detecting infections among both the vaccinated and unvaccinated individuals.
This analysis lead to the finding that in the presence of vaccines, the CFR depends not only on the effectiveness of vaccines in preventing deaths but also on the detection of breakthrough infections. As a result, a decline in the CFR may not imply that vaccines are effective in reducing deaths. Likewise, a constant CFR can still mean that vaccines are effective in reducing deaths. Furthermore, this allows the conclusion that unless vaccinated people are also tested for COVID-19 infection, the CFR loses its meaning in tracking the pandemic. This shows that unless efforts are directed at detecting breakthrough infections, it is hard to disentangle the effect of vaccines in reducing deaths from the probability of detecting infections on the CFR.
di Lego, V., Sanchez-Romero, M., & Prskawetz, A. (2022). The impact of COVID-19 vaccines on the Case Fatality Rate: The importance of monitoring breakthrough infections. International Journal of Infectious Diseases 119 178-183. 10.1016/j.ijid.2022.03.059.