Effectiveness of seasonal influenza vaccine against clinically diagnosed influenza over 2 consecutive seasons in children in Guangzhou, China

Abstract

Influenza vaccine has to be reformulated each year due to the ever-changing antigenicity of the influenza virus. However, few post-licensure studies of influenza vaccine are available in China. We aimed to measure the effectiveness of seasonal influenza vaccine during 2 consecutive seasons. Among children in Guangzhou aged 6 to 59 mo in 2010–2012, we matched each child with clinically diagnosed influenza to 3 healthy children. Cases with clinically diagnosed influenza were identified from surveillance system. Healthy controls were randomly sampled from the Children’s Expanded Programmed Immunization Administrative Computerized System. Conditional logistic regression was used to calculate vaccine effectiveness (VE). A total of 275 matched sets of subjects were included. VE levels against clinically diagnosed influenza for both seasons combined was 47.4% [95% confidence interval (CI), 8.5–69.8%] for full vaccination for children aged 6–35 mo, 33.6% (95% CI, 5.4–53.5%) for any vaccination for children aged 6–59 mo, respectively. VE by time since vaccination for any vaccination was 34.6% (95% CI, 4.7–55.2%) in 0–5 mo, and no protection was observed in 6–11 mo. Annual, full and timely vaccination should be encouraged for children.

Keywords: :

• seasonal influenza
• vaccine
• case-control studies
• children
• China

Funding

This work was supported by grants from the Guangdong Provincial Department of Science and Technology (2011B050300001 and 2012B091100045), Science and Information Technology of Guangzhou (2012J5100005).

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

We highly appreciate the help from the physicians from sentinel surveillance hospitals for this study and Guangzhou CDC. We are also indebted to the parents for their participation.