Investigating vaccine preventable diseases and outbreaks in Australia

Abstract

Despite having a well-established and successful National Immunisation Program (NIP), vaccine preventable diseases continue to affect communities and result in large outbreaks in Australia. Because of the dynamic nature of vaccine preventable diseases, surveillance and monitoring of epidemiological trends are necessary for informing appropriate policy development and vaccine delivery. In this thesis, I present selected works under the theme of the epidemiology of vaccine preventable diseases which I conducted while placed at the National Centre for Immunisation Research and Surveillance (NCIRS) from March 2012-2014 as a Master of Philosophy Applied Epidemiology (MAE) Scholar. The works presented comprise my MAE requirements, of which a core component is to investigate an outbreak. My first outbreak investigation was a foodborne outbreak of staphylococcal gastroenteritis at an elite athletic event, where fried rice and chicken were suspected as the cause. The remainder of my MAE work related to vaccine preventable diseases and I participated in the public health response to a state-wide outbreak of measles, including a specific investigation to determine the source of infection for a cluster of four cases infected in a paediatric hospital Emergency Department (ED). I developed an algorithm for this contact tracing investigation, although the source of infection was never identified. Measles was also the subject of my applied epidemiological project, where I considered characteristics of measles in the post-elimination era with an emphasis on the role of healthcare setting transmissions in perpetuating outbreaks. In the 2012 outbreak, 16 individuals infected with measles transmitted the illness to 36 others in EDs and General Practice (GP) clinics. In addition, I examined the vaccine effectiveness of the measles vaccine that may allow outbreaks to persist in a setting of high vaccine coverage. I analysed pertussis trends in Australia from 2006-2012, which revealed that the average annual notification rate was more than 2.8 times that of the previous decade with a significant change in the pattern of age-specific incidence. The steepest increases in notification rates were among children less than 10 years, especially those 2-4 years and 6-9 years of age. Reasons for this shift include increased diagnostic testing and more rapid waning of effectiveness post vaccination with acellular vaccines compared to whole cell vaccines used in previous decades. The shift was exacerbated by cessation of the 18 month dose in the National Immunisation Program (NIP) from 2003. Lastly, I evaluated Australia's post-marketing surveillance for intussusception following the introduction of the rotavirus vaccines in 2007. The evaluation found that despite not having planned surveillance, Australian systems evolved to include several surveillance components that were more effective than the nation's passive adverse event following immunisation (AEFI) surveillance system at detecting cases and assessing causality. The work in this thesis contributed to the work of NCIRS and improves our understanding of the epidemiology of vaccine preventable diseases in Australia. Show more