Preventive Efficacy of Influenza Vaccination against to Influenza-like Illness among Eldery

Chun, Byung Chul; Woo, Heung Jeong; Park, Seung Chul

Abstract

BACKGROUND: Influenza is a highly infectious viral illness. The epidemics of influenza occur from the late fall to the early spring nearly every year and are responsible for several hundred thousand death per year all over the world. Influenza vaccine is the primary method for preventing influenza and its more severe complications. The efficacy of influenza vaccination have been well known in developed countries. The influenza vaccination has been recommended as one of the tentative immunization schedule for indicated persons since 1997 in Korea. But there are still no available data about them, even though nearly 5 - 8 million doses of influenza vaccine were used in a winter season. PURPOSE: To assess the clinical efficacy of influenza vaccine against influenza-like illness(ILI) among Korean elderly(age over 65). METHODS: Primary study design - a prospective field trial. Study subjects and method - We prospectively observed the 1,488 vaccinee and 1,425 non-vaccinee in a community(Nonsan city) from November 1 1998 to March 31 1999. The vaccinee were those who randomly selected 100-200 per 13 sub-region(Myon) in Nonsan city, and the non-vaccinee were those who had not vaccinated until January 1999 among the Nonsan city elderly cohort. This cohort was consisted of 5,787 elderly(over 1/3 of total elderly population) who had ever visited the community health center or 13 public health offices in Nonsan city in 1998. We followed up these two groups two times-in January and April 1999 - by telephone survey. The questionnaire included the questions about the health behaviors, medical history, socioeconomic condition, medical security type, physical function status, medical facility utilization in the season, symptom and signs of influenza-like illness, number and type of the flu, hospitalization or not. We did throat swap to isolate the virus of 490 patient who had influenza -like symptoms in the same period. RESULTS: Influenza vaccination was significantly reduced the incidence of influenza -like illness(fever or chilling sensation and cough or sore throat) in the vaccinated. The preventive effect of influenza-like illness among influenza risk group was about 32%(95% CI, 20%-44%). The illness duration of main symptoms of influenza-like illness(fever, cough) was significantly shorter in the vaccinee. The consistency of the survey was noted quite high from the analysis of the result of test-retest(104 person). CONCLUSION: Influenza vaccination significantly reduced the incidence of influenza-like illness(32%) among elderly.