Serological protection against influenza and cardiovascular events in cardiac ICU patients during seasonal epidemics

BACKGROUND AND OBJECTIVES: Influenza can be associated with acute cardiovascular events, but the impact of serological protection in high-risk patients admitted to Cardiac Intensive Care Units (C-ICUs) is unknown. This study aimed to analyze previous vaccination rate, level of serological protection and laboratory-confirmed influenza, among patients admitted to C-ICUs during influenza season, and its association with cardiovascular events. METHODS: Prospective multicenter study of all patients admitted to C-ICUs during 2017-2018, 2018-2019, and 2019-2020 influenza seasons. A systematic search for influenza was performed using the Xpert Xpress Flu/RSV assay (Cepheid, Sunnyvale, CA, USA). The seroprotection rate was assessed by analyzing the percentage of patients with antibody titers against influenza ≥1/40, and the intensity of seroprotection by evaluating the geometric mean titers of these antibodies. RESULTS: From 397 patients, 245 (61.7%) reported previous influenza vaccine. A total of 23 patients had laboratory-confirmed influenza (23/397, 5.8%). Overall, the seroprotection rate was significantly higher for influenza A than for B (84.6% vs 37.5%, P < 0.001) and higher in vaccinated than in non-vaccinated group. The highest seroprotection rate and intensity was observed for subtype A(H3N2), followed by A(H1N1)pdm09, B/Victoria, and finally B/Yamagata. Compared unvaccinated patients, those with prior vaccination had lower rates of ST-segment elevation myocardial infarction (28.2% vs 40.8%, P = 0.009), pulmonary embolism (0.8% vs 4.6%, P = 0.014), and severe clinical presentation (53.1% vs 67.1%, P = 0.006). CONCLUSIONS: Serological protection was higher against influenza A than B, especially for the A (H3N2) subtype. ST-segment elevation myocardial infarction, pulmonary embolism, and severe clinical presentation appear to be reduced with influenza vaccination.