Background: There are controversies about vaccination effectiveness of seasonal influenza and its wide variation across seasons and countries. Objectives: This study aimed to estimate the effectiveness of seasonal influenza vaccination among adult population in Tabuk City, Saudi Arabia.
Methods: This prospective cohort study included residents aged 18 years or older. 532 participants were divided regarding vaccination status into two equal groups: the first (vaccine group) received the current influenza vaccine, and the other (control group) received nothing. Data were collected through a structured questionnaire. The vaccine effectiveness was estimated based on self-reported data regarding the incidence of chest infection or flu-like illness (FLI) after the vaccination, duration of the FLI, ability to do the normal daily activity, seeking medical care, need for visiting a clinic, taking medications, and hospital admissions.
Results: The rate of chest infection after vaccination showed no significant difference between the two groups (p=0.879). The incidence of FLI in winter following vaccine intake was significantly higher in the vaccine group compared to the control (p=0.038). The FLI affected the daily life activities of 36 subjects (13.5%) belonging to the vaccine group compared to 28 subjects (10.5%) in the control group (p=0.286). Seeking medical service for the FLI was recorded in 7.5% and 4.5% of the vaccine and the control groups, respectively, with no significant difference (p=0.145).
Conclusions: The seasonal flu vaccine lacked significant effectiveness among adult population in Tabuk City, Saudi Arabia. Regularly improving the immunogenicity and efficacy of influenza vaccines seems a necessity.