Impacts of influenza vaccination policy for the elderly and the SARS epidemic on influenza-like illness in Taiwan

Abstract

The effectiveness of influenza vaccination on influenza-like illness (ILI) incidences has been controversial, and requires further studies. In Taiwan, a severe infectious disease epidemic, for example, the severe acute respiratory syndrome (SARS) has been speculated to have impacts on ILI incidences, which has not yet been systematically assessed. This study evaluates the impacts of influenza vaccination policy for the elderly (age ≥ 165 yrs) and the SARS epidemic on ILI in Taiwan by using the weekly ILI surveillance data reported by sentinel physicians in Taiwan.

The data were reported by sentinel physicians across all cities and counties in Taiwan. An autoregressive-integrated moving average (ARIMA) model with intervention analysis, which is also referred to impact analysis, was employed to evaluate the impacts of these events. The impact estimates were jointly estimated with outlier effects and other model parameters.

The estimates of the two event impacts are statistically significant (p-value < 0.05) and both have negative values. The effect estimate of the influenza vaccination policy was –5.4847 case-counts per sentinel physician (95% CI = (–9.9561, –2.0133), p-value < 0.001). As for the impact of the SARS epidemic, it also had a statistically significant level reduction of 4.7040 case-counts (95% CI = (–8.1869, –1.2211), p-value < 0.005).

The influenza vaccination policy for the elderly and the SARS epidemic have resulted in statistically significant reductions of ILI incidences in Taiwan. These results May provide empirical evidences for other countries on assessing the impacts of these two events.

Keywords and phrases:

• Influenza vaccination
• influenza-like illness
• SARS
• ARIMA model
• intervention
• outlier