Using Laboratory-Confirmed Outcomes to Study Pediatric Influenza and Influenza Vaccine Epidemiology in Ontario Using Laboratory-Confirmed Outcomes to Study Pediatric Influenza and Influenza Vaccine Epidemiology in Ontario
Annual epidemics of seasonal influenza continue to cause substantial morbidity in young children. Influenza is among several respiratory viruses that cause illness in children, in addition to a large burden on the healthcare system and society, but is the only one for which a vaccine is available. In this dissertation, I present three studies regarding the epidemiology of influenza in children under the age of five years using a novel approach of linking laboratory and health administrative data in Ontario. In a systematic review and meta-analysis of children presenting to healthcare who are tested for influenza, I found that 20% (95%CI 15%-25%) have laboratory-confirmed influenza, with variation across subgroups. I found that influenza represents a large overall burden of disease and a substantial proportion of healthcare encounters for respiratory illnesses. In a retrospective cohort study, I compared the characteristics, outcomes, and relative severity of illness of children who were hospitalized and tested for influenza A, influenza B, and respiratory syncytial virus (RSV) and were positive for only a single virus. I found that in-hospital outcomes and post-discharge healthcare utilization in children with no identified comorbidities were similar by virus type, but post-discharge healthcare utilization was higher for those with influenza in those with underlying comorbidities. I observed similar severity of illness, based on in-hospital outcomes, and cost of hospitalization between viruses. In a test-negative study, I estimated vaccine effectiveness (VE) against laboratory-confirmed influenza hospitalizations in children aged 6-59 months for the 2010-11 to 2013-14 seasons. I found that overall, VE was 51% (95%CI 38%-61%) for any vaccination, with variation by vaccination status (full vs. partial), season, age group, and subtype. These results indicate that large numbers of pediatric hospitalizations resulting from influenza infection could be prevented by promoting seasonal influenza vaccination each year. Overall, these results contribute to our understanding of pediatric respiratory viruses in Ontario, with each individual chapter adding to our knowledge regarding burden, severity, and prevention of influenza infection. These results can inform families, clinicians, public health practitioners, and policy makers in order to help reduce the impact of annual influenza infection in young children.
Annual epidemics of seasonal influenza continue to cause substantial morbidity in young children. Influenza is among several respiratory viruses that cause illness in children, in addition to a large burden on the healthcare system and society, but is the only one for which a vaccine is available. In this dissertation, I present three studies regarding the epidemiology of influenza in children under the age of five years using a novel approach of linking laboratory and health administrative data in Ontario. In a systematic review and meta-analysis of children presenting to healthcare who are tested for influenza, I found that 20% (95%CI 15%-25%) have laboratory-confirmed influenza, with variation across subgroups. I found that influenza represents a large overall burden of disease and a substantial proportion of healthcare encounters for respiratory illnesses. In a retrospective cohort study, I compared the characteristics, outcomes, and relative severity of illness of children who were hospitalized and tested for influenza A, influenza B, and respiratory syncytial virus (RSV) and were positive for only a single virus. I found that in-hospital outcomes and post-discharge healthcare utilization in children with no identified comorbidities were similar by virus type, but post-discharge healthcare utilization was higher for those with influenza in those with underlying comorbidities. I observed similar severity of illness, based on in-hospital outcomes, and cost of hospitalization between viruses. In a test-negative study, I estimated vaccine effectiveness (VE) against laboratory-confirmed influenza hospitalizations in children aged 6-59 months for the 2010-11 to 2013-14 seasons. I found that overall, VE was 51% (95%CI 38%-61%) for any vaccination, with variation by vaccination status (full vs. partial), season, age group, and subtype. These results indicate that large numbers of pediatric hospitalizations resulting from influenza infection could be prevented by promoting seasonal influenza vaccination each year. Overall, these results contribute to our understanding of pediatric respiratory viruses in Ontario, with each individual chapter adding to our knowledge regarding burden, severity, and prevention of influenza infection. These results can inform families, clinicians, public health practitioners, and policy makers in order to help reduce the impact of annual influenza infection in young children.