SODAS Talk

The vaccine effectiveness fallacy

Robert Böhm, RWTH Aachen Universitet, is visiting SODAS and will be presenting at a SODAS Talk Tuesday the 27th of November 2018.

Abstract

Vaccination provides direct benefits for the vaccinating individuals by reducing the likelihood of contracting infectious diseases at marginal costs. In addition, most vaccines provide indirect benefits for unvaccinated individuals by reducing the spread of pathogens in the population (herd immunity). When considering both its direct and indirect benefits, individuals have an incentive to free-ride on others’ indirect protection with increasing vaccination rates. Previous research on interactive vaccination decisions assumed explicitly or implicitly that vaccinations protect effectively against contracting diseases, i.e., in 100% of the vaccinations. However, this is virtually never achieved and the effectiveness of vaccines varies widely.

In the present research, we theoretically analyse the behavioural consequences of ineffective (vs. effective) vaccines in a game-theoretical framework of interactive vaccination decisions. We find that ineffective vaccines increase the individual incentives for vaccination because the indirect benefits of herd immunity decrease. To investigate the effect of vaccine (in)effectiveness on vaccination behaviour empirically, we conducted two online experiments using convenience samples of the normal population (N = 358) and health care workers (N = 138). We observe a vaccine effectiveness fallacy: participants reduce their vaccination intentions with decreasing vaccine effectiveness. In a second step, we conducted an additional laboratory experiment (N = 288), implementing an interactive vaccination game with monetary incentives. In contrast to the surveys, participants received full information about the direct and indirect effect of vaccinations and the corresponding consequences of decreasing vaccine effectiveness. Results show that vaccination becomes more likely when participants face an ineffective (vs. effective) vaccine, eliminating the vaccine effectiveness fallacy. We discuss the implications for vaccination policy and potential interventions to increase vaccine uptake.  

The SODAS Talk will take place in building 35, 2^nd floor, room 36 (35.2.36) of the CSS Campus, Copenhagen University, from 10.30am - 11.30am.

If you have questions or want to know more, please write Agnete Vienberg Hansen at avh@econ.ku.dk.