Elsevier

Vaccine

Volume 25, Issue 5, 15 January 2007, Pages 846-855
Vaccine

Influenza- and RSV-associated hospitalizations among adults

https://doi.org/10.1016/j.vaccine.2006.09.041Get rights and content

Abstract

We estimated influenza- and respiratory syncytial virus (RSV)-associated hospitalizations by age, high-risk status and outcome, during the 1996/1997–1999/2000 respiratory seasons among adults who did not receive influenza vaccine. Using three health maintenance organization (HMO) databases and local viral surveillance data, we identified weeks when influenza and RSV were circulating and estimated influenza- and RSV-associated hospitalizations. Persons aged ≥65 years with and without high-risk conditions had significantly increased rates of influenza-associated hospitalizations for pneumonia and influenza, and circulatory and respiratory diseases. Persons aged ≥65 years with high-risk conditions also had significantly increased rates of influenza-associated hospitalizations for cardiac conditions (16.9 per 10,000 person periods). Relative to the influenza estimates for high-risk persons ≥65 years, we found lower rates of RSV-associated hospitalizations for pneumonia and influenza diseases (23.4 per 10,000 person periods), cardiac diseases (4.3 per 10,000 person periods) and circulatory and respiratory diseases (44.0 per 10,000 person periods). Among low-risk persons aged 50–64 years, we did not identify significantly elevated rates of influenza- or RSV-associated hospitalizations. Excess hospitalization estimates among adults aged ≥65 years and high-risk 50–64 year olds during the influenza season suggest that these groups should have priority for influenza vaccine during vaccine shortages.

Section snippets

Background

Influenza viruses are associated with illness among all age groups, but the risk of serious illness and death following infection is highest among persons aged ≥65 years and persons with certain chronic medical conditions. These groups have been targeted for influenza vaccination in the United States since the early 1960s [1]. In 2000, the US Center for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices (ACIP) expanded their influenza vaccination recommendations

Population

The study populations included adult members of three large west coast HMOs that participate in the CDC-sponsored Vaccine Safety Datalink Project (VSD): Kaiser Permanente Northwest (KPNW), Portland, Oregon metropolitan area; Kaiser Permanente Northern California (KPNC), Northern California; Group Health Cooperative (GHC), Seattle, WA metropolitan area. The goals, structure and data resources of the VSD have been described previously [30].

We examined four respiratory seasons (i.e. 1996/1997,

Results

KPNC had the largest population of the three HMOs and contributed the majority of the person–time data (Table 1). More than one-half of the person–time data came from persons aged 18–49 years. Unvaccinated high-risk person–time was greatest among persons aged ≥65 years, while unvaccinated low-risk person–time was greatest among persons aged 18–49 years.

The weekly percentages of specimens that tested positive for influenza and RSV are plotted in Fig. 1 for GHC, Fig. 2 for KPNC and Fig. 3 for

Discussion

We compared rates of influenza-associated hospitalizations among unvaccinated adults in three age groups (18–49, 50–64 and ≥65 years). During our study period, ACIP recommendations for influenza vaccination differed among these age groups, with annual vaccination recommended only for all those aged ≥65 years. There are few available data concerning excess hospitalizations associated with influenza among adults in the 18–49 and 50–64 age groups.

In contrast with non-high-risk persons 65 years and

Acknowledgements

We thank CDC's Influenza and Respiratory and Enteric Viruses Branches for access to the influenza and RSV circulation data used in this study. We are grateful to Jen Coury for editorial assistance. Supported by CDC contract no. 200-2002-00732. The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the funding agency.

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