Health sustainability in times of disease outbreak is linked to the communication effectiveness of public health messages. Where the pathogenicity of a disease is more harmful to the immunity level of some individuals during an outbreak, the design of health advisory messages constitute a powerful influence in understanding the disease and behaviour change in specific contexts of vulnerability during the  outbreaks. Drawing on the Yale attitude change model and the health belief model, this chapter examined the communication effectiveness of the media information available to those with compromised immunity due to old age or non-communicable diseases. The findings showed that the effectiveness of media health advisory messages depended on whether their communicative qualities were appropriate for the audience. The credibility of the source of the information, audience characteristics embedded in the messages and the behavioural interventions were predictive of compliance with the messages. The chapter recommended health advisory messages designed aligned to behaviour change models.