27307102

PMC5021558

Background

The Thai Advisory Committee on Immunization Practices recommends annual influenza vaccination for children six months through two years of age, although older children may be vaccinated on request. We evaluated effectiveness of the 2013 and 2014 inactivated influenza vaccines to reduce medically-attended laboratory-confirmed influenza illness among Thai children aged 7–60 months.

Methods

From September 2013–May 2015, children with influenza-like illness (ILI) were screened with a rapid influenza diagnostic test. Enrolled children had nasal and throat swabs tested for influenza viruses using polymerase chain reaction (PCR). Cases and controls were subjects testing positive and negative, respectively, for influenza viruses by PCR. Vaccination status was ascertained from vaccination cards. Vaccine effectiveness (VE) was calculated as 100%*(1−odds ratio of vaccination among cases versus controls).

Results

Of 1,377 children enrolled, cases (n=490) and controls (n=887) were similar in demographic characteristics. Cases were less likely to receive influenza vaccine than controls in 2013 (6% vs. 14%; p=0.02), but not in 2014 (6% vs. 7%; p=0.57). Among cases, 126 (26%) were positive for influenza A(H1N1)pdm09 virus, 239 (49%) for influenza A(H3N2) and 124 (25%) for influenza B. One specimen was positive for both influenza A(H3N2) and B viruses. VE for full vaccination against all viruses was 64% (95% confidence interval [CI], 21%, 84%) in 2013 and 26% (95% CI, −47%, 63%) in 2014.

Conclusions

Influenza vaccination was low among Thai children in our study, and VE varied by year, highlighting the need for annual monitoring of VE to better understand vaccine program effectiveness.

CDC Public Access

U01 GH000152/GH/CGH CDC HHS/United States