Estimating vaccine-prevented disease outcomes when vaccination has only direct effects

Vaccination is a useful tool for reducing the burden of infectious diseases. One way to quantify the benefits of vaccination is to estimate the number of health outcomes prevented by vaccination. This article improves a method described by Foppa et al., which assumes that vaccination has only direct effects, meaning it cannot prevent infection or onward transmission of the disease. The new, improved method increases estimation accuracy with minimal additional analytical complexity. To evaluate this method, disease outbreaks were simulated, and the accuracy of both methods was compared. In most simulations, specifically in 84%, the improved method had an equal or smaller estimation error compared to the original Foppa method. The mean error was 7.9-fold smaller, and the standard deviation of errors was 44-fold smaller. This study thus improves a method for estimating prevented disease burden under the assumption that vaccination has only direct effects.