Pandemic vaccination strategies and influenza severe outcomes during the influenza A(H1N1)pdm09 pandemic and the post-pandemic influenza season: the Nordic experience.
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.
Statens Serum Institut, Copenhagen, Denmark.
Julita
J
Gil Cuesta
Preben
P
Aavitsland
Hélène
H
Englund
Ólafur
Ó
Gudlaugsson
Siri Helene
SH
Hauge
Outi
O
Lyytikäinen
Guðrún
G
Sigmundsdóttir
Anders
A
Tegnell
Mikko
M
Virtanen
Tyra Grove
TG
Krause
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype; D007252:Influenza Vaccines / Q000627:therapeutic use; D007251:Influenza, Human / Q000401:mortality* / Q000517:prevention & control* / Q000821:virology; D007362:Intensive Care Units / Q000706:statistics & numerical data; D008297:Male; D032541:Mass Vaccination / Q000379:methods / Q000401:mortality / Q000706:statistics & numerical data*; D008875:Middle Aged; D058873:Pandemics / Q000517:prevention & control* / Q000706:statistics & numerical data*; D011247:Pregnancy; D015995:Prevalence; D012307:Risk Factors; D012537:Scandinavian and Nordic Countries / Q000453:epidemiology; D012621:Seasons; D012720:Severity of Illness Index; D015996:Survival Rate; D016896:Treatment Outcome; D055815:Young Adult
D007252:Influenza Vaccines
Pandemics; influenza A(H1N1)pdm09; influenza A(H3N2); influenza B virus; influenza virus; intensive care units; vaccines and immunisation