Efficacy and effectiveness of influenza vaccination
Introduction
Influenza continues to be a major cause of morbidity and mortality, and vaccination remains the mainstay of efforts to prevent and control influenza. In the United States inactivated influenza vaccines have been available for more than 50 years, and since 2003 a live attenuated influenza vaccine has also been available. Current recommendations of the US Advisory Committee on Immunization Practices (ACIP) for the prevention and control of influenza have identified high-priority groups that should be targeted for annual vaccination, although all persons wishing to avoid influenza are encouraged to receive the vaccine [1]. These high-priority groups, representing nearly 3/4 of the US population, include persons at increased risk for complications of influenza as well as persons likely to transmit influenza to other high-risk persons [2]. With the recent expansion of recommendations to include all children up to age 18 years, the percentage of person in the US included among the high-priority groups will be even higher. Many other countries recommend annual vaccination for the elderly and others with high-risk medical conditions, with several also recommending routine vaccination for young children, healthcare workers, and other groups [3]. This report will summarize recent data on the efficacy and effectiveness of inactivated and live attenuated influenza vaccines among children and adults. It is beyond the scope of this paper to include data on novel new vaccines such as those that contain adjuvants.
Section snippets
Definitions
Before reviewing studies assessing vaccine efficacy and effectiveness, it is important to review clinical outcome definitions and their implications for vaccine efficacy and effectiveness results. Studies of influenza vaccine efficacy and effectiveness have often used a variety of outcomes or case definitions that can dramatically affect the numbers reported and how we interpret them. Some of these outcomes include infection rates, illness rates (clinical versus laboratory confirmed illness)
Influenza vaccine efficacy/effectiveness study results
Recent systematic reviews have provided summary findings of the efficacy and effectiveness of influenza vaccination among children, healthy younger adults, community-dwelling elderly and elderly residing in nursing homes. This paper will rely heavily on these systematic reviews, most of which are formal meta-analyses, and most of which rely heavily on randomized controlled trials – the gold standard study design. These reviews were identified through online literature searches (Medline &
Summary and conclusion
Influenza remains a major cause of morbidity and mortality. Currently available influenza vaccines provide substantial protection against influenza among children and young, healthy adults and against the serious complications of influenza including hospitalization and death among the elderly. Current US vaccination rates for all high-priority groups remain well below national goals, and globally, vaccine distribution rates in many countries suggest that vaccine delivery is suboptimal in
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