Pandemic influenza 2009: Impact of vaccination coverage on critical illness in children, a Canada and France observational study

AIM: To study the impact of vaccination critical illness due to H1N1pdm09, we compared the incidence and severity of H1N1pdm09 infection in Canada and France. METHODS: We studied two national cohorts that included children with documented H1N1pdm09 infection, admitted to a pediatric intensive care unit (PICU) in Canada and in France between October 1, 2009 and January 31, 2010. RESULTS: Vaccination coverage prior to admission to PICUs was higher in Canada than in France (21% vs 2% of children respectively, P < 0.001), and in both countries, vaccination coverage prior to admission of these critically ill patients was substantially lower than in the general pediatric population (P < 0.001). In Canada, 160 children (incidence = 2.6/100000 children) were hospitalized in PICU compared to 125 children (incidence = 1.1/100000) in France (P < 0.001). Mortality rates were similar in Canada and France (4.4% vs 6.5%, P = 0.45, respectively), median invasive mechanical ventilation duration and mean PICU length of stay were shorter in Canada (4 d vs 6 d, P = 0.02 and 5.7 d vs 8.2 d, P = 0.03, respectively). H1N1pdm09 vaccination prior to PICU admission was associated with a decreased risk of requiring invasive mechanical ventilation (OR = 0.30, 95%CI: 0.11-0.83, P = 0.02). CONCLUSION: The critical illness due to H1N1pdm09 had a higher incidence in Canada than in France. Critically ill children were less likely to have received vaccination prior to hospitalization in comparison to general population and children vaccinated had lower risk of ventilation.