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Influenza virus infections from 0 to 2 years of age: A birth cohort study
Tamara Teros-Jaakkola1, Laura Toivonen1, Linnea Schuez-Havupalo1
1Department of Paediatrics and Adolescent Medicine, Turku University Hospital and University of Turku, Turku, Finland.
Insights
This study found that the yearly incidence of seasonal influenza in young children was around 5%, with varying vaccine coverage. The adjuvanted pandemic influenza vaccine proved highly effective, and most cases were not severe.
Area of Science:
- Pediatric infectious diseases
- Vaccinology
- Epidemiology
Background:
- Influenza vaccination is recommended for children in Finland since 2007 (6-35 months) and 2009 (≥6 months).
- Understanding influenza incidence and vaccine effectiveness in young children is crucial for public health strategies.
Purpose of the Study:
- To investigate the incidence of influenza in a Finnish birth cohort of children aged 6-35 months.
- To evaluate the effectiveness of influenza vaccines in this pediatric population between 2008 and 2011.
Main Methods:
- A birth cohort of 923 children was followed for respiratory tract infections until age 2.
- Nasal swabs were collected for PCR testing of influenza A and B viruses.
- Vaccination data was obtained from national health registries.
Main Results:
- Influenza incidence varied by season, ranging from 2.7% to 5.1% annually.
- Vaccination coverage for seasonal influenza was 22-47%, and 80% for pandemic A(H1N1)pdm09.
- The adjuvanted pandemic influenza vaccine demonstrated 97% effectiveness against A(H1N1)pdm09; only three hospitalizations occurred.
Conclusions:
- Seasonal influenza affects approximately 5% of very young children annually.
- The adjuvanted pandemic influenza vaccine was highly effective in preventing illness.
- Both seasonal and pandemic influenza infections in this cohort were generally mild.
Background/Purpose:
Influenza vaccine has been recommended in Finland since 2007 for all children of 6-35 months of age and in 2009 for those ≥6 months against pandemic influenza. We investigated the incidence of influenza and vaccine effectiveness in a birth cohort of children in 2008-2011.
Methods:
We followed 923 children from birth to 2 years of age for respiratory tract infections. A nasal swab sample for PCR for influenza A and B viruses was taken at the onset of acute respiratory infections. Samples were collected either at the study clinic or at home by parents. Vaccination data was retrieved from the health registries.
Results:
Vaccination coverage of children aged 6-23 months was 22-47% against seasonal influenza and 80% against the A(H1N1)pdm09 virus in the pandemic season 2009-2010. During 3 influenza seasons, 1607 nasal swab samples were collected. Influenza was confirmed in 56 (6.1%) of 923 children (16 A(H1N1), 14 A(H3N2), and 26 B viruses). The incidence of influenza was 5.1% in 2008-2009, 2.7% in 2009-2010, and 5.0% in 2010-2011. Effectiveness of the adjuvanted vaccine against the pandemic influenza A(H1N1)pdm09 was 97% (95% confidence interval, 76-100%). Three children with influenza were hospitalized.
Conclusion:
The yearly incidence of seasonal influenza was 5% in this cohort of very young children with variable influenza vaccine coverage. Adjuvanted vaccine against the pandemic influenza was highly effective. Both seasonal and pandemic influenza cases were mostly non-severe.
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