BACKGROUND:
Influenza vaccinations play an important role in preventing influenza related hospitalizations. The objective of this study was to estimate the effectiveness of vaccination in protecting Beijing residents aged ≥60?years from influenza related hospitalizations during the 2016/17 and 2017/18 influenza seasons.
METHODS:
Patients who met the definition of severe acute respiratory infection (SARI) and were hospitalized in the nine sentinel hospitals in Beijing during the 2016/17 and 2017/18 influenza seasons were identified as the study population. The vaccination status of patients was obtained from a vaccination registry. Real-time reversetranscription polymerasechainreaction (RT-PCR) experiments were conducted to test pharyngeal or lower respiratory tract samples collected from SARI patients for influenza A and B viruses. Vaccine effectiveness (VE) was examined using a test-negative design that compare the odds of vaccination among influenza positives and negatives, adjusting for calendar week of illness onset, age, and underlying medical conditions.
RESULTS:
We identified 50,364 patients in the study, in which there were 145 influenza cases and 528 influenza-negative controls aged ≥60?years in 2016/17 season and 149 cases and 358 controls aged ≥60?years in 2017/18 season. The most commonly identified subtype among participants was influenza A(H3N2) in 2016/17 and 2017/18 season (78.5% and 70.6%). Among the adults aged ≥60?years, the adjusted VE of vaccination against any influenza virus for serious acute respiratory infection (SARI) patients was 32.8% (95% confidence interval [CI]: -22.0 to 63.0%) in 2016/17 season. While the adjusted VE in 2017/18 season were 4.6% (95% CI: -72.4 to 47.2%) against any types of influenza, 29.2% (95% CI: -92.9 to 74%) against influenza A(H1N1)pdm09, -37.7% (95% CI: -293.8; 51.9%) against influenza A(H3N2) viruses, and 3.6% (95% CI: -113.8 to 56.5%) against influenza B.
CONCLUSION:
The influenza vaccine provided moderate protection in 2016/17 season and mild protection in 2017/18 season for influenza related inpatients of adults aged ≥60?years in Beijing.