Kristin Greve-Isdahl Mohn, Birger N Lærum, Steinar Skrede, Rebecca J Cox, Anne Ma Dyrhol-Riise, Hans Erling Simonsen, Nina Langeland, Jörg A&beta, Jörg Aβmus, Per-Espen Akselsen, Haakon Sjursen and Ingrid Smith
Background: Norway had a pre-order of vaccine, when the pandemic influenza A (H1N1)pdm09 in 2009 was declared. Mass vaccination occurred 1-3 weeks prior to the peak of the pandemic. Emergency plans were in place, but the predicted severe numbers of hospitalizations did not occur. Objective: To study the epidemiology and clinical presentation of adult patients hospitalized with influenza A (H1N1) pdm09, and to evaluate the impact of vaccination on the course of the pandemic at a tertiary hospital. Methods: The low dose oil-in-water adjuvanated vaccine was used to vaccinate healthcare workers (HCWs) and at risk patients groups, and vaccination rates were recorded for the community and the hospital. Demographic and clinical information was obtained for 129 patients (>15 years), hospitalized with influenza A (H1N1)pdm09 between August 2009-January 2010. A confirmed case of influenza A (H1N1)pdm09 was defined as meeting a clinical case definition and/or laboratory confirmed disease (rt-PCR or serology). Hospital stay of more than 2 days was defined as a sign of severe illness. Results: 1/3 of at risk patients in the community and >90% of frontline HCWs at the hospital were vaccinated. The median length of hospital stay of infected patients was significantly reduced 7 days after the onset of mass vaccination (p=0.029). There was a predominance of female and moderately obese (BMI 25-30) patients. Infiltration on chest X-ray upon admission was significantly associated with a hospital stay of >2 days (p=0.001). Conclusion: Mass vaccination of frontline HCWs at the hospital and at risk patients in the community contributed to the observed significant reduction in hospital stay of patients infected with influenza. Almost no absenteeism enabled staff confidence and the ability for quick and safe patient turnover. This study highlights the importance of early influenza vaccination, to protect the high-risk patients and the integrity of the healthcare system.