Vaccination against influenza A(H1N1)pdm09 in Japan started in October 2009. Children with asthma are considered as a high-risk group and are recommended to preferentially receive the vaccine.
To identify the clinical effects of vaccination in Japanese children with and without asthma.
We conducted a cross-sectional, questionnaire-based survey to compare vaccination rates, vaccine effectiveness against physician-diagnosed influenza A infection (PDIA), and consecutive asthma exacerbations between children with and without asthma.
Of the 460 children included in this study, those with asthma had higher vaccination rates (46.5%, 67/144) than those without asthma (30.4%, 96/316). Influenza A infections were diagnosed in 28 of 163 vaccinated children (17.2%) compared to 164 of 297 unvaccinated children (55.2%, p < 0.001). Comparison of positive influenza diagnosis rates between vaccinated and unvaccinated children with and without asthma showed that unvaccinated children with asthma had an elevated odds ratio (13.235; 95% confidence interval [CI], 5.564-32.134) and that treatment for asthma exacerbations was needed in a larger proportion of unvaccinated children. Vaccine effectiveness against PDIA was 87% (95% CI, 78-93%) overall, 92% (95% CI, 81-96%) in children with asthma and 81% (95% CI, 63-91%) in children without asthma, respectively.
The administration of an inactivated, split-virus, non-adjuvanted monovalent A(H1N1)pdm09 vaccine during the pandemic period reduced the number of physician-diagnosed influenza A infections and asthma exacerbations in children with asthma. Therefore, we strongly recommend that high-risk children with a history of asthma receive vaccines during pandemics.