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Long term effectiveness of adjuvanted influenza A(H1N1)pdm09 vaccine in children
Åke Örtqvist1, Rutger Bennet2, Johan Hamrin2
1Karolinska Institutet, Department of Medicine, Unit of Infectious Diseases, Karolinska Solna, Stockholm, Sweden; Department of Communicable Disease Control and Prevention, Stockholm County Council, Box 175 33, SE-118 91 Stockholm, Sweden.
Insights
The Pandemrix vaccine (AS03 adjuvanted H1N1) effectively protected children against severe influenza A(H1N1)pdm09 hospitalization for at least two seasons. This vaccine demonstrated significant effectiveness in preventing serious illness in pediatric populations.
Area of Science:
- * Pediatric Infectious Diseases
- * Vaccinology
- * Epidemiology
Background:
- * The AS03 adjuvanted monovalent influenza A(H1N1)pdm09 vaccine (Pandemrix) was administered to 69% of children in Stockholm County during the 2009 pandemic.
- * Immunological data suggested a potentially longer duration of effectiveness for AS03-adjuvanted vaccines compared to non-adjuvanted seasonal influenza vaccines.
- * Influenza A(H1N1)pdm09 was the predominant strain during the 2009-2010 season, with A(H3N2) circulating in 2011-2012.
Purpose of the Study:
- * To evaluate the effectiveness of the Pandemrix vaccine in preventing influenza A(H1N1)pdm09 hospitalizations in children.
- * To assess the vaccine's effectiveness during the 2010-2011 and 2012-2013 influenza seasons.
Main Methods:
- * A retrospective case-control study utilizing a modified test-negative design.
- * Comparison of Pandemrix vaccination rates between children diagnosed with influenza A(H1N1)pdm09 (cases) and those with influenza A(H3N2) or influenza B (controls).
- * Exclusion of children born after July 1, 2009, to focus on the eligible age group for the pandemic vaccine.
Main Results:
- * In the 2010-2011 season, vaccine effectiveness (VE) against influenza A(H1N1)pdm09 hospitalization was 91.7% (OR 0.083; 95% CI 0.014, 0.36).
- * During the 2012-2013 season, no significant difference in vaccination status was observed between influenza A(H1N1)pdm09 cases and controls (59-60% vaccinated).
- * Vaccination rates with Pandemrix in 2009 were 19% for influenza A(H1N1)pdm09 cases versus 78% for influenza A(H3N2)/B controls in 2010-2011.
Conclusions:
- * The AS03 adjuvanted influenza A(H1N1)pdm09 vaccine (Pandemrix) demonstrated significant effectiveness in preventing pediatric hospital admissions for influenza A(H1N1)pdm09.
- * The vaccine's protective effect was sustained for at least two influenza seasons post-administration.
- * Findings support the long-term benefit of adjuvanted pandemic influenza vaccines in children.
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.
