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Comparative Study
. 2015 May 21;33(22):2558-61.
doi: 10.1016/j.vaccine.2015.04.011. Epub 2015 Apr 11.

Long term effectiveness of adjuvanted influenza A(H1N1)pdm09 vaccine in children

Åke Örtqvist  1 , Rutger Bennet  2 , Johan Hamrin  2 , Malin Ryd Rinder  3 , Hans Lindblad  4 , Joanna Nederby Öhd  5 , Margareta Eriksson  2
Affiliations
Comparative Study

Long term effectiveness of adjuvanted influenza A(H1N1)pdm09 vaccine in children

Åke Örtqvist et al. Vaccine. .

Abstract

Background: Immunological studies have indicated that the effectiveness of AS03 adjuvanted monovalent influenza A(H1N1)pdm09 vaccine (Pandemrix) may be of longer duration than what is seen for non-adjuvanted seasonal influenza vaccines. Sixty-nine percent of children 6 months-18 years of age in Stockholm County received at least one dose of Pandemrix during the 2009 pandemic. We studied the effectiveness of the vaccine during the influenza seasons 2010-2011 and 2012-2013 in children hospitalized with virologically confirmed influenza. The season 2011-2012 was not included, since influenza A(H3N2) was the predominant circulating strain.

Methods: In a retrospective case-control study using a modified test-negative design we compared the percentage vaccinated with Pandemrix among children diagnosed with influenza A(H1N1)pdm09 (cases), with that of those diagnosed with influenza A(H3N2) or influenza B (controls) during the two seasons. We excluded children born after July 1, 2009, since only children who were 6 months of age or older received the pandemic vaccine in October-December 2009.

Results: During the 2010-2011 season, 3/16 (19%) of children diagnosed with influenza A(H1N1)pdm09, vs. 32/41 (78%) of those with influenza A(H3N2) or influenza B had been vaccinated with Pandemrix in 2009. The odds ratio, after adjustment for sex, age and underlying diseases, for becoming a case when vaccinated with Pandemrix was 0.083 (95%CI 0.014, 0.36), corresponding to a VE of 91.7%. During the season 2012-2013, there was no difference between the two groups; 59% of children diagnosed with influenza A(H3N2)/B and 60% of those with influenza A(H1N1)pdm09 had been vaccinated with Pandemrix in 2009.

Conclusion: The AS03 adjuvanted monovalent influenza A(H1N1) pdm09 vaccine (Pandemrix) was effective in preventing hospital admission for influenza A(H1N1)pdm09 in children during at least two seasons.

Keywords: Children; Effectiveness; Long term; Pandemic; Vaccination.

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