"Influenza-associated morbidity and mortality increase with age, especially for individuals with high-risk conditions," the authors note. "The effectiveness of vaccination has been reported to decrease in high-risk persons. Annual influenza revaccination has been proposed as a strategy to increase vaccination effectiveness."

Second Time Around

In this study, A.C.G. Voordouw, M.D., from Erasmus Medical Center, Rotterdam, The Netherlands, and colleagues analyzed data from 1996 through 2002 from electronic patient records that were part of the Integrated Primary Care Information Project of Medical Informatics at the Erasmus Medical Center.

The study included 26,071 persons aged 65 years or older. During the total study period, they received 62,476 influenza vaccinations. The annual vaccination coverage ranged from 64 percent in 1996 to 74 percent in 1999. Influenza epidemics during the study period were of mild to moderate severity with the 2000 - 2001 season showing no clear epidemic activity.

During the study followup period, 3,485 patients died. "Overall, a first vaccination was associated with a nonsignificant annual reduction of mortality (death) risk of 10 percent, while revaccination was associated with a reduced mortality risk of 24 percent," the authors report.

"Compared with a first vaccination, revaccination was associated with a reduced annual mortality risk of 15 percent," they continue. "During the epidemic periods this reduction was 28 percent."

Consistency Counts

The authors also found that an interruption of the annual vaccinations series was associated with a 25 percent increase in mortality risk, whereas restarting vaccination after an interruption resulted in a mortality risk reduction similar to that observed following revaccination. The authors note that "in the total population one death was prevented for every 302 vaccinations, or 1 for every 195 revaccinations."

"In summary, our study shows that annual revaccination against influenza in a population of community-dwelling elderly persons is associated with a reduction of mortality risk," the authors conclude. "This study supports the recommendation for yearly influenza vaccination for elderly individuals, not only for those with comorbid illness but also in those without comorbidity and in patients 80 years or older. Because influenza vaccination is inexpensive and safe, clinicians should recommend annual influenza revaccination for such patients."