Influenza Vaccine Effectiveness in Preventing Outpatient, Inpatient, and Severe Cases of Laboratory-Confirmed Influenza

Abstract

Influenza vaccination prevented influenza cases and hospitalizations and was associated with a better prognosis in inpatients with influenza. The combined effect of these 2 mechanisms would explain the high effectiveness of the vaccine in preventing severe cases due to influenza.

Repeated influenza vaccination for preventing severe and fatal influenza infection in older adults: a multicentre case–control study

“…This definition has relevant implications, is easy to apply and to compare, and has been used previously. 5,8,11,12 We compared baseline characteristics between patients with influenza and controls, patients with nonsevere and severe illness, and vaccinated and unvaccinated patients with influenza. We used the χ 2 and Fisher exact tests for categorical variables and the t test for continuous variables.…”

“…1,2 Influenza vaccination is effective in preventing visits to primary health care and hospital admissions for laboratory-confirmed influenza, [3][4][5][6] but there is little research available on the effectiveness of influenza vaccination on severe and fatal laboratoryconfirmed influenza. 5 Age-related changes in the immune system, major chronic conditions and risk factors may interfere with and hamper a successful vaccine response in older adults.…”

“…5 Age-related changes in the immune system, major chronic conditions and risk factors may interfere with and hamper a successful vaccine response in older adults. 7 When influenza vaccination fails to prevent illness caused by influenza, studies have suggested that vaccination may still have an additional effect by reducing the severity of disease.…”

“…7 When influenza vaccination fails to prevent illness caused by influenza, studies have suggested that vaccination may still have an additional effect by reducing the severity of disease. 5,[8][9][10][11][12][13] This vaccine effect would be of great interest among older adults, in whom the effectiveness of influenza vaccination is normally suboptimal and severe influenza is more frequent. 1,6,7 Influenza vaccination in previous seasons may retain some preventive effectiveness, [14][15][16][17] and new doses may boost the preexisting immune memory against antigenically related strains.…”

Influenza and pneumococcus vaccination: current recommendations

“…A single dose of an influenza vaccine should be offered soon after the vaccine becomes available, ideally by October in the northern hemisphere and May in the southern hemisphere. Influenza virus usually causes an acute self-limited illness in healthy young adults, however, older adults and patients with different health problems are high risk groups [7,8]. The United States Advisory Committee on Immunization Practices (ACIP) expanded the recommendation for influenza vaccination to include all individuals six months of age and older.…”