Effectiveness of Influenza Vaccine in Older People
A Cohort Study of the Effectiveness of Influenza Vaccine in Older People, Performed Using the United Kingdom General Practice Research Database. Mangtani P, Cumberland P, Hodgson CR, Roberts JA, Cutts FT, and Hall AJ. The Journal of Infectious Diseases 2004;190:1-10
Explanatory note: Influenza causes hospitalizations and death, especially among individuals older than 64 years. Trivalent inactivated influenza vaccine (TIV) reduces complications from influenza, including death. The impact of TIV immunization programs on preventing death and hospitalizations has been difficult to assess because many deaths in this age group are due to pneumonia or underlying medical conditions and because TIV immunization is not routinely documented. Although universal TIV immunization has been recommended for older Americans for many years, this recommendation was not made in the United Kingdom (UK) until 1998 (for those older than 75 years) and then was expanded in 2000 to all for those older than 64 years. Thus prior to then, it is likely that most TIV immunizations in the UK were given to those with high-risk medical conditions.
How effective has vaccination with TIV been for persons who are more than 64 years of age in the decade leading up to the recommendation for universal TIV immunization in the UK?
This study analyzed data from individuals older than 64 years of age available in the General Practice Research Database in England and Wales for 1989 to 1999.
The researchers divided the population into those who had been vaccinated (692,819 person-years) and not vaccinated (1,534,280 person-years). They then identified how many persons in each group were admitted to the hospital for acute respiratory illnesses (for example, influenza, bronchitis, pneumonia) and all who died who had any respiratory disease at the time of death.
The groups were also divided according to those at high risk for complications of influenza—those with underlying medical conditions such as chronic lung disease—and those at lower risk—those that did not have a risk factor other than age.
The researchers noted that the number of repeated prescriptions for drugs for different conditions during the year allowed them to assess for the presence and severity of underlying illnesses.
The rate of TIV immunization increased over the period of 10 years from 18% to 42.6%. Those who had received TIV were more likely to be older and to have high-risk medical conditions. During the study period, they were also more likely to have been hospitalized for acute respiratory disease and to have died from respiratory related causes.
When the analyses were adjusted for the differences in underlying medical conditions and the ages of the groups, influenza vaccine was found to have been 21% effective in protecting against hospitalizations for acute respiratory disease and 12% effective in preventing deaths due to respiratory disease.
TIV was effective in mild as well as severe influenza seasons. Both those with and those without high-risk medical conditions benefitted from TIV immunization.
TIV had no effect on mortality or hospitalization rates except during the season when influenza infections were occurring. Thus, during the influenza season, there were 4.15 fewer hospitalizations per week for every 100,000 persons.
The relevance/bottom line
Influenza vaccination reduced the number of hospitalizations and deaths due to respiratory disease in individuals more than 64 years of age—whether or not they had high-risk conditions other than age. These findings were observed both in years of severe and mild influenza activity.
Universal TIV for individuals over 64 years is of benefit.
In the United States universal TIV immunization is recommended for all persons over 49 years of age and those 6 to 23 months of age in addition for all with underlying medical conditions.
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