EFFICACY AND EFFECTIVINESS OF INACTIVED INFLUENZA VIRUS VACCINE

Factors influencing vaccine efficacy Closeness of the match between the vaccine strain and the circulating virus Age of vaccinee: older people do not respond as well Health of the vaccinee: people with chronic illnesses and immune system disorders do not respond as well as healthy individuals Number of vaccinations – regular annual vaccinations improve the protection compared with the first year of vaccination Type of vaccine used

Efficacy of influenza vaccination in healthy adults Prevention of influenza infection –Recommended inactivated parenteral vaccines Efficacy: 70% Effectiveness: 25% –Recommended live aerosol vaccines Efficacy: 48% Effectiveness: 15% Demicheli V et al. Cochrane Database Syst Rev 2004; 3: CD

Efficacy of influenza vaccination in elderly and high-risk persons Prevention of illness and death –Among high-risk adults (e.g. patients with chronic cardiovascular, respiratory or renal disease) 18– 64 years, vaccination prevented: 1 78% of deaths 87% of hospitalisations 26% of GP visits –Among elderly individuals (> 65 years), vaccination prevented: 1 50% of deaths 48% of hospitalisations 1. Hak E et al. Arch Intern Med 2005; 165: 274–80

Efficacy of influenza vaccination in elderly and high-risk persons Prevention of illness and death –Among community-dwelling elderly individuals, influenza vaccination prevented 1 death for every 302 vaccinees at vaccination coverage between 64% and 74% Voordouw AC et al. JAMA 2004; 292: 2089–95.

Efficacy of influenza vaccination in elderly persons In a meta-analysis of 20 cohort studies, pooled estimates of vaccine efficacy demonstrated prevention of morbidity and mortality during the influenza season –Respiratory illness56% –Pneumonia53% –Hospitalisation50% –Death68% Gross PA et al. Ann Intern Med 1995; 123: 518–27. The studies confirm the effectiveness of influenza vaccine

Influenza deaths versus vaccination history WHO Collaborating Centre for Influenza, Melbourne. Odds ratio – influenza death Previous only 1985–88 First vaccination 1989 Vaccinated 1989 and previously Regular annual vaccination improves protection

Influenza vaccination in patients with CHD Case control study of 218 patients with coronary heart disease (CHD) during the 1997–98 influenza season in the USA Efficacy of influenza vaccine in reducing the risk of recurrent myocardial infarction (MI) in patients with CHD Past and current influenza vaccination reduces the risk of recurrent MI in CHD patients Correlation between different factors and the risk of recurrent MI ORCorrelation Current hypertension Hypercholesterolemia Smoking Influenza vaccination Vaccination associated with a reduced risk of recurrent MI Naghavi M et al. Circulation 2000; 102: 3039–45.

Influenza vaccination in individuals with asthma No significant increase in asthma exacerbations in the 2 weeks following influenza vaccination –Based on pooled results of two trials involving 2306 individuals with asthma in a Cochrane review No significant reduction in influenza-related asthma exacerbations –Based on a recent study of 696 children with asthma Cates CJ et al. Cochrane Database Syst Rev 2004; 2: CD

Years of life bought for US$1 million (1990 dollars) Pap smear every 3 years 52 life-years Bypass surgery for left main 134 life-years coronary artery disease Pneumococcal pneumonia 100 life-years vaccination Influenza vaccination11,100 life-years Influenza vaccination is a highly cost-effective healthcare intervention Russell LB. Health Aff (Millwood) 1992; 11: 162–9.

By courtesy of APACI Asia-Pacific Advisory Committee on influenza