Tuesday, November 3, 2009
Effectiveness of Flu Vaccine
The CDC claims that studies demonstrate that vaccination can be a cost-effective counter-measure to seasonal outbreaks of influenza; but not perfect. A study led by Dr. David K. Shay in February, 2008 reported that
"full immunization against flu provided about a 75 percent effectiveness rate in preventing hospitalizations from influenza complications in the 2005-6 and 2006-7 influenza seasons."
Modern influenza vaccines have been criticized for a lack of effectiveness demonstrated in controlled studies. A 2006 Cochrane review of influenza vaccination in the elderly stated "The apparent high effectiveness of the vaccines in preventing death from all causes may reflect a baseline imbalance in health status and other systematic differences in the two groups of participants.
A study on selection bias for influenza vaccine in the elderly found that it could account for the entirety of the protective effect. A 2008 Cochrane review of healthy children found "Influenza vaccines are efficacious in children older than two but little evidence is available for children under two." . The CDC recommends every child over 6 months be given the influenza vaccine. A 2007 Cochrane review on influenza vaccines in healthy adults found that while vaccines were effective against the influenza strains they are designed to vaccinate against, this ended up translating to only a modest impact on working days lost due to influenza-like infections.
The group most vulnerable to flu, the elderly, is also the least affected by the vaccine, with an average efficacy rate ranging from 40-50% at age 65, and 15-30% past age 70. There are multiple reasons behind this steep decline in vaccine efficacy, the most common of which are the declining immunological function and frailty associated with advanced age.
In the United States a person aged 50–64 is nearly ten times more likely to die an influenza-associated death than a younger person, and a person over age 65 is over ten times more likely to die an influenza-associated death than the 50–64 age group. Vaccination of those over age 65 reduces influenza-associated death by about 50%. However, it is unlikely that the vaccine completely explains the results since elderly people who get vaccinated are probably more healthy and health-conscious than those who do not. Elderly participants randomized to a high-dose group (60 micrograms) had antibody levels 44 to 79 percent higher than did those who received the normal dose of vaccine. Elderly volunteers receiving the higher dose were more likely to achieve protective levels of antibody.
Information obtained from:
Margy Wienbar, Region Director
Public Health Regions 1,3
New Mexico Department of Health
1111 Stanford Dr NE
Albuquerque, NM 87106
FAX (505) 841-4147