The impact of psychology on the effectiveness of voluntary vaccination against infectious diseases in networks

Behaviour is often neglected when modelling vaccination policies. This thesis shows the importance of incorporating behaviour in vaccination models of the impact of vaccines on disease dynamics. This thesis consists of three projects pertaining to voluntary vaccination in a network setting. The first project focuses on the effectiveness of voluntary ring vaccination under the presence of imitation. The contacts of a single index case vaccinate when symptoms first appear. We assume the contacts are unable to transmit infection to one another; however, we assume they are able to share their vaccination strategies. Under the presence of strong imitation, the effectiveness of voluntary ring vaccination becomes unpredictable. The second project focuses on the impact of personal experiences on voluntary influenza vaccination in a uniform network. Vaccination behaviour is based upon past infection and vaccination experiences, which creates a feedback loop between incidence and behaviour. Long-term memory acts as a stabilizing factor; however, long-term memory also decreases perceived vaccine efficacy. Vaccines conferring slowly waning immunity decrease vaccination coverage, leading to sporadic outbreaks in the absence of non-influenzal influenza-like-illness (niILI). Our results show evidence of vaccination strategy correlations being formed in the absence of imitation through past experiences. Allowing niILI to be mistaken for true influenza breaks up the strategy correlations, while stabilizing dynamics. The final model focuses on vaccination strategies targeting superspreaders, with the option of distributing economic incentives. We take a more psychological approach to influenza vaccination behaviour, where transmission of influenza occurs on an empirically based network. On average, superspreaders view the vaccine to be less effective; however, superspreaders still find vaccination more appealing because they are at a greater risk of becoming infected. The incorporation of behaviour leads to superspreader strategies to become less effective due to policy resistance; neglecting behaviour can lead to an overestimation of reduction of incidence. Public health officials should be concerned about the policy resistance and decreased perceived vaccine efficacy among superspreaders. The effectiveness of the vaccination or control policies could be diminished by the presence of behaviour, even when pro-active preventative measures are implemented by public health.