Factors associated with infection by 2009 pandemic H1N1 influenza virus during different phases of the epidemic

Day Yu Chao, Kuang Fu Cheng, Tsai Chung Li, Trong Neng Wu, Chiu Ying Chen, Chen An Tsai, Jin Hua Chen, Hsien Tsai Chiu, Jang Jih Lu, Mei Chi Su, Yu Hsin Liao, Wei Cheng Chan, Ying Hen Hsieh

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

Abstract

Objective: The focus of this study was to ascertain the factors associated with 2009 pandemic influenza H1N1 (pH1N1) infection during different phases of the epidemic. Methods: In central Taiwan, 306 persons from households with schoolchildren were followed sequentially and serum samples were taken at three sampling time-points starting in the fall of 2008, shortly after influenza vaccination. Participants who seroconverted between two consecutive blood samplings were considered as having serological evidence of infection. A generalized estimation equation (GEE) with a logistic link to account for household correlations was applied to identify factors associated with pH1N1 infections during the pre-epidemic (April-June) and epidemic (September-October) periods. Results: The results showed that receiving an inactivated seasonal influenza vaccine (ISIV) and having a hemagglutination inhibition assay (HI) titer of 40 or higher resulted in a significantly lower likelihood of pH1N1 infection during the pre-epidemic period only, for both children and adults (adjusted odds ratio (OR) 0.3, 95% confidence interval (CI) 0.12-0.9). Having a previous infection by pH1N1 with a baseline titer of 20 or higher resulted in a significantly lower likelihood of infection by pH1N1 during the epidemic period (adjusted OR 0.06, 95% CI 0.02-0.16). Conclusions: Our results provide the first serological evidence to suggest a protection effect from receiving an ISIV against pH1N1 infection only when the HI titer reaches 40 or higher during the pre-epidemic period. This study gives an important insight into the control and intervention measures required for preventing infections during future influenza epidemics.

Original languageEnglish
JournalInternational Journal of Infectious Diseases
Volume15
Issue number10
DOIs
Publication statusPublished - Oct 2011
Externally publishedYes

Keywords

  • 2009 H1N1
  • Pandemic
  • Protection factors
  • Risk factors
  • Serology
  • Transmission

ASJC Scopus subject areas

  • Microbiology (medical)
  • Infectious Diseases

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