Pandemic vaccination strategies and influenza severe outcomes during the influenza A(H1N1)pdm09 pandemic and the post-pandemic influenza season:the Nordic experience

• Published in: Eurosurveillance
• Main Authors: Gil Cuesta, Julita, Aavitsland, Preben, Englund, Hélène, Gudlaugsson, Olafur, Hauge, Siri Helene, Lyytikäinen, Outi, Sigmundsdóttir, Guðrún, Tegnell, Anders, Virtanen, Mikko, Krause, Tyra Grove, Fischer, Thea Kølsen
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Adolescent; Adult; Aged; 80 and over; Child; Preschool; Female; Hospitalization; Humans; Infant; Influenza A Virus; H1N1 Subtype; Influenza Vaccines; Influenza; Human; Intensive Care Units; Male; Mass Vaccination; Middle Aged; Pandemics; Pregnancy; Prevalence; Risk Factors; Scandinavian and Nordic Countries; Seasons; Severity of Illness Index; Survival Rate; Treatment Outcome; Young Adult; Comparative Study; Journal Article; Iceland
• Online Access: https://portal.findresearcher.sdu.dk/da/publications/f50808d5-9286-4d08-91ae-2ba04f1ae455; https://doi.org/10.2807/1560-7917.ES.2016.21.16.30208; https://findresearcher.sdu.dk/ws/files/129612381/Pandemic_vaccination_strategies_and_influenza_severe_outcomes_during_the_influenza_A_H1N1_pdm09_pandemic_and_the_post_pandemic_influenza_season.pdf

During the 2009/10 influenza A(H1N1)pdm09 pandemic, the five Nordic countries adopted different approaches to pandemic vaccination. We compared pandemic vaccination strategies and severe influenza outcomes, in seasons 2009/10 and 2010/11 in these countries with similar influenza surveillance systems. We calculated the cumulative pandemic vaccination coverage in 2009/10 and cumulative incidence rates of laboratory confirmed A(H1N1)pdm09 infections, intensive care unit (ICU) admissions and deaths in 2009/10 and 2010/11. We estimated incidence risk ratios (IRR) in a Poisson regression model to compare those indicators between Denmark and the other countries. The vaccination coverage was lower in Denmark (6.1%) compared with Finland (48.2%), Iceland (44.1%), Norway (41.3%) and Sweden (60.0%). In 2009/10 Denmark had a similar cumulative incidence of A(H1N1)pdm09 ICU admissions and deaths compared with the other countries. In 2010/11 Denmark had a significantly higher cumulative incidence of A(H1N1)pdm09 ICU admissions (IRR: 2.4; 95% confidence interval (CI): 1.9-3.0) and deaths (IRR: 8.3; 95% CI: 5.1-13.5). Compared with Denmark, the other countries had higher pandemic vaccination coverage and experienced less A(H1N1)pdm09-related severe outcomes in 2010/11. Pandemic vaccination may have had an impact on severe influenza outcomes in the post-pandemic season. Surveillance of severe outcomes may be used to compare the impact of influenza between seasons and support different vaccination strategies.