title: The impact of matching vaccine strains and post-SARS public health efforts on reducing influenza-associated mortality among the elderly.
abstract: Public health administrators do not have effective models to predict excess influenza-associated mortality and monitor viral changes associated with it. This study evaluated the effect of matching/mismatching vaccine strains, type/subtype pattern changes in Taiwan's influenza viruses, and the impact of post-SARS (severe acute respiratory syndrome) public health efforts on excess influenza-associated mortalities among the elderly. A negative binomial model was developed to estimate Taiwan's monthly influenza-associated mortality among the elderly. We calculated three winter and annual excess influenza-associated mortalities [pneumonia and influenza (P&I), respiratory and circulatory, and all-cause] from the 1999-2000 through the 2006-2007 influenza seasons. Obtaining influenza virus sequences from the months/years in which death from P&I was excessive, we investigated molecular variation in vaccine-mismatched influenza viruses by comparing hemagglutinin 1 (HA1) of the circulating and vaccine strains. We found that the higher the isolation rate of A (H3N2) and vaccine-mismatched influenza viruses, the greater the monthly P&I mortality. However, this significant positive association became negative for higher matching of A (H3N2) and public health efforts with post-SARS effect. Mean excess P&I mortality for winters was significantly higher before 2003 than after that year [mean +/- S.D.: 1.44+/-1.35 vs. 0.35+/-1.13, p = 0.04]. Further analysis revealed that vaccine-matched circulating influenza A viruses were significantly associated with lower excess P&I mortality during post-SARS winters (i.e., 2005-2007) than during pre-SARS winters [0.03+/-0.06 vs. 1.57+/-1.27, p = 0.01]. Stratification of these vaccine-matching and post-SARS effect showed substantial trends toward lower elderly excess P&I mortalities in winters with either mismatching vaccines during the post-SARS period or matching vaccines during the pre-SARS period. Importantly, all three excess mortalities were at their highest in May, 2003, when inter-hospital nosocomial infections were peaking. Furthermore, vaccine-mismatched H3N2 viruses circulating in the years with high excess P&I mortality exhibited both a lower amino acid identity percentage of HA1 between vaccine and circulating strains and a higher numbers of variations at epitope B. Our model can help future decision makers to estimate excess P&I mortality effectively, select and test virus strains for antigenic variation, and evaluate public health strategy effectiveness.
authors.affiliation: Institute of Epidemiology, College of Public Health, National Taiwan University, Taipei, Taiwan.
authors.forename: Ta-Chien
authors.initials: TC
authors.lastname: Chan
authors.forename: Chuhsing Kate
authors.initials: CK
authors.lastname: Hsiao
authors.forename: Chang-Chun
authors.initials: CC
authors.lastname: Lee
authors.forename: Po-Huang
authors.initials: PH
authors.lastname: Chiang
authors.forename: Chuan-Liang
authors.initials: CL
authors.lastname: Kao
authors.forename: Chung-Ming
authors.initials: CM
authors.lastname: Liu
authors.forename: Chwan-Chuen
authors.initials: CC
authors.lastname: King
mesh_terms: D000368:Aged; D006801:Humans; D007252:Influenza Vaccines / Q000008:administration & dosage*; D007251:Influenza, Human / Q000401:mortality / Q000517:prevention & control* / Q000821:virology; D011159:Population Surveillance; D015980:Public Health Practice; D045169:Severe Acute Respiratory Syndrome / Q000453:epidemiology
chemical_list: D007252:Influenza Vaccines