A note on the impact of a behavioral side-effect of vaccine failure on the spread of a contagious disease

Vaccines do save lives; however, no vaccine provides complete immunity for all vaccinated individuals. Thus, some individuals remain susceptible to the contagious disease against which they were vaccinated. By relying on the supposed acquired immunity, these individuals can reduce the self-imposed prevention measures and, as a consequence, they can involuntarily promote the spread of the infection. Here, such individuals are taken into account in an epidemic model based on ordinary differential equations. Depending on the parameter values related to contagion and vaccine efficacy, a less responsible behavior post-vaccination can increase the basic reproduction number of the disease as compared to the case with no vaccine. This result is discussed by considering the current COVID-19 outbreak.

Automated summary

Vaccines can save lives, but not all vaccinated individuals achieve complete immunity. Some individuals may still be susceptible to the disease they were vaccinated against, and if they rely solely on acquired immunity, they may inadvertently contribute to the spread of infection. Irresponsible behaviors post-vaccination can lead to an increase in the basic reproduction number of the disease, compared to scenarios where no vaccine is available. The implications of this are discussed in the context of the current COVID-19 outbreak.