Influenza Vaccination Responses in Disabled Stroke Patients: A Single-Center Prospective Observational Study

This study aimed to investigate the immunological response to influenza vaccination, the incidence and severity of influenza infection, and the side effects of the vaccination in patients with ischemic stroke.

This prospective observational study was conducted between 2023 and 2024 at Ramathibodi Hospital. Enrolled patients received standard doses of inactivated trivalent influenza vaccine. Seroprotection and seroconversion were assessed using hemagglutination inhibition tests before (T0) and 4-8 weeks (T1) after vaccination. Additional clinical information was gathered, and adverse events were monitored.

In total, 161 individuals completed the hemagglutination inhibition analysis. The mean ages (±SD) of the control, functionally independent, and functionally dependent groups were 69.40 (±7.40) years, 71.40 (±8.60) years, and 75.90 (±8.30) years, respectively (p < 0.001). The proportion of participants with hemagglutination inhibition titers greater than 1:40 for the A/Sydney (H1N1) strain was significantly greater in the functionally independent group than in the functionally dependent group (p = 0.031 at T0 and p = 0.003 at T1). The seroconversion rates were significantly higher in the control group than in the functionally independent or functionally dependent group (34.20% vs. 25.40% vs. 19.40%, p = 0.033). The overall incidence rate of probable influenza was 6.2 cases per 100 person-years, and no serious adverse events related to vaccination were reported.

The rates of seroprotection were higher for the functionally independent group than for the functionally dependent group. Therefore, the functionally dependent group may require a modified influenza vaccination strategy to achieve more effective immune responses.