Impacts of a mass vaccination campaign against pandemic H1N1 2009 influenza in Taiwan: a time-series regression analysis.
OBJECTIVE
A multicenter, hospital-wide, clinical and epidemiological study was conducted to assess the effectiveness of the mass influenza vaccination program during the 2009 H1N1 influenza pandemic, and the impact of the prioritization strategy among people at different levels of risk.


RESULTS
Among the 34 359 medically attended patients who displayed an influenza-like illness and had a rapid influenza diagnostic test (RIDT) at one of the three participating hospitals, 21.0% tested positive for influenza A. The highest daily number of RIDT-positive cases in each hospital ranged from 33 to 56. A well-fitted multiple linear regression time-series model (R(2)=0.89) showed that the establishment of special community flu clinics averted an average of nine cases daily (p=0.005), and an increment of 10% in daily mean level of population immunity against pH1N1 through vaccination prevented five cases daily (p<0.001). Moreover, the regression model predicted five-fold or more RIDT-positive cases if the mass influenza vaccination program had not been implemented, and 39.1% more RIDT-positive cases if older adults had been prioritized for vaccination above school-aged children.


CONCLUSIONS
Mass influenza vaccination was an effective control measure, and school-aged children should be assigned a higher priority for vaccination than older adults during an influenza pandemic.
Department of Internal Medicine, National Taiwan University Hospital, 7 Chung-Shan South Road, Zhongzheng District, Taipei 100, Taiwan.
Un-In
UI
Wu
Department of Internal Medicine, National Taiwan University Hospital, 7 Chung-Shan South Road, Zhongzheng District, Taipei 100, Taiwan.
Jann-Tay
JT
Wang
Department of Internal Medicine, National Taiwan University Hospital, 7 Chung-Shan South Road, Zhongzheng District, Taipei 100, Taiwan; Center for Infection Control, National Taiwan University Hospital, Taipei, Taiwan.
Shan-Chwen
SC
Chang
Department of Internal Medicine, National Taiwan University Hospital, 7 Chung-Shan South Road, Zhongzheng District, Taipei 100, Taiwan.
Yu-Chung
YC
Chuang
Department of Internal Medicine, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan.
Wei-Ru
WR
Lin
Department of Internal Medicine, Chung-Shan Medical University Hospital, Taichung, Taiwan.
Min-Chi
MC
Lu
Department of Internal Medicine, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan.
Po-Liang
PL
Lu
Graduate Institute of Clinical Medicine and School of Nursing, College of Medicine, National Taiwan University, Taipei, Taiwan.
Fu-Chang
FC
Hu
Taiwan Centers for Disease Control, Taipei, Taiwan.
Jen-Hsiang
JH
Chuang
Department of Internal Medicine, National Taiwan University Hospital, 7 Chung-Shan South Road, Zhongzheng District, Taipei 100, Taiwan; Center for Infection Control, National Taiwan University Hospital, Taipei, Taiwan. Electronic address: yeechunchen@gmail.com.
Yee-Chun
YC
Chen
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D016021:Epidemiologic Studies; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000175:diagnosis / Q000453:epidemiology* / Q000517:prevention & control; D016014:Linear Models; D032541:Mass Vaccination / Q000379:methods*; D008875:Middle Aged; D058873:Pandemics; D013624:Taiwan / Q000453:epidemiology; D055815:Young Adult
Effectiveness; Influenza; Mass vaccination; Pandemic; Prioritization; Time-series regression analysis