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2003-04 Trivalent inactivated influenza vaccine (TIV) effectiveness: A retrospective cohort study at The Children's Hospital (TCH), Denver, Colorado

Marika K. Iwane, PhD MPH1, Nidhi Jain, MD, MPH1, Susan Dolan, RN, MS, CIC2, Carolyn Bridges, MD1, Paul Gargiullo, PhD1, John R. Copeland, MS1, Felicita David, MS1, Kristin Kenyan, RN, MPH1, Zack Moore, MD, MPH1, Ann-Christine Nyquist, MD MPH2, James Todd, MD2, Jim Alexander, MD MPH1, and Jane Seward, MBBS MPH1. (1) National Immunization Program, Centers for Disease Control and Prevention, 1600 Clifton Rd, MS E61, Atlanta, GA 30333, 404-639-8769, miwane@cdc.gov, (2) Department of Epidemiology, The Children's Hospital, 1056 East 19th Avenue, B276, Denver, CO 80218

Objectives: The 2003-04 influenza season was characterized by widespread activity in early November in parts of the country. Additionally, the predominant influenza A/H3N2 virus circulating was antigenically distinct from the H3N2 vaccine strain. To estimate the vaccine effectiveness (VE) of the 2003-04 TIV, we conducted a rapid assessment among hospital employees using a retrospective cohort study design.

Methods: Influenza viruses circulated at high levels among TCH’s patients November 1- December 27, 2003. During December 11-17, we asked TCH employees to complete a questionnaire on influenza vaccination and influenza-like illness (ILI). ILI was defined as subjective fever plus cough or sore throat after November 1st. The exposure cohort time was November 1 until the survey completion date or an ILI. We determined vaccinated and unvaccinated person-time and conducted two analyses considering person-time 0-13 days after vaccination as a)unvaccinated or b)excluded. VE was calculated as [1- Incidence Rate Ratio (IRR)]; IRR equals ILI incidence rate among vaccinated/ ILI incidence rate among unvaccinated.

Results: Of 3100 employees, 1886 (61%) responded. Of these, 1424 (78%) received TIV, with 1009 (71%) vaccinated before November 1st. ILI was self-reported by 217 (16%) respondents. VE estimates were a) -0.10 [95% Confidence interval (CI)= -0.41 to +0.14] and b) -0.15 (95%CI= -0.52 to +0.13) adjusted for age group, high-risk conditions, and patient contact.

Conclusions: In this rapid assessment, we demonstrated no VE of TIV against ILI. However, VE against severe illness or laboratory-confirmed influenza is likely to be higher. Prospective VE studies with laboratory-confirmed outcomes are optimal and should be conducted annually.

Learning Objectives:

Presenting author's disclosure statement:
I do not have any significant financial interest/arrangement or affiliation with any organization/institution whose products or services are being discussed in this session.

Vaccine Preventable Diseases

The 132nd Annual Meeting (November 6-10, 2004) of APHA