Annual influenza vaccination of patients with cardiovascular diseases and changes in hemagglutinin antibody titers: 3-year follow-up data

Abstract

BACKGROUND: Seasonal influenza vaccination is recommended for patients with cardiovascular diseases. Low vaccination coverage among these patients is due to insufficient knowledge about vaccine efficiency and its regular annual use.
 This work aimed to study the repeated 6-month changes in hemagglutinin antibody titers (AT) for 3 years in patients with cardiac pathology in a comparative study of influenza preventive vaccination.
 MATERIALS AND METHODS: Analysis of ATs obtained based on the hemagglutination-inhibition test (HAI) was performed in 235 of 817 participants in a prospective follow-up. Blood sampling was performed at baseline, before the vaccination, and 6 months after, and at the same term in unvaccinated patients in the 20122013 and 20142015 seasons, respectively. The seropositive and seronegative responses to vaccination or acute respiratory or influenza infection were used, according to the reference values of seroconversion and seroprotection and the fact of seroconversion. Multiple regression analysis with a logarithmic scale was used to assess the vaccine effectiveness indices.
 RESULTS: With vaccination coverage of at least 40% against seasonal influenza within 3 years, the trends of a decrease in seropositive and an increase in seronegative responses in the vaccination group and its reverse nature in the comparison group were determined by traditional analysis. Using logarithmic calculation, an increase in HAI AT seroconversion was revealed over a 3-year follow-up period. It was characterized by a homogeneous serological response at annual vaccination and heterogeneous with a higher serological response in cases without vaccination (p = 0.002 for H1N1 and p = 0.005 for H3N2, respectively). This trend can be determined by a higher and more stable prevaccination level of HAI AT than the same residual level of AT among unvaccinated patients.
 CONCLUSION: During long-term cardiac studies, the logarithmic calculation in interpreting the results of HAI AT overcomes the limitations of the traditional analysis of assessing the efficiency of the annual influenza vaccine. Further serological programs are required to better understand the role of routine seasonal influenza vaccination in preventing morbidity and mortality of patients with cardiovascular diseases.