TOPLINE:

Among patients admitted to cardiac ICUs, influenza vaccination was associated with stronger serological protection, especially against subtype A(H3N2), and lower rates of ST‑segment elevation myocardial infarction, pulmonary embolism, and severe clinical presentation during seasonal epidemics.

METHODOLOGY:

• This prospective multicentre study in Spain assessed the proportion of prior influenza vaccination, serological protection, and laboratory-confirmed influenza and examined their association with cardiovascular events in 397 patients (median age, 67.0 years; 67.3% men) admitted to cardiac ICUs during influenza seasons from 2017 to 2020.
• Nasopharyngeal specimens were tested for influenza A and B viruses using the Xpert Xpress Flu/RSV assay; serum was analysed for antibodies against influenza using the haemagglutination inhibition assay.
• The seroprotection rate was assessed as the proportion of patients with antibody titres of ≥ 1:40, and the seroprotection intensity was evaluated by assessing geometric mean titres of these antibodies.
• Severe clinical presentation criteria included conditions such as pneumonia, myocarditis, pericarditis, heart failure, ischaemic events, cardiac arrhythmias, and/or multiorgan failure.

TAKEAWAY:

• Overall, 61.7% of patients reported prior seasonal influenza vaccination; 5.8% had laboratory-confirmed influenza, all of which were influenza A virus.
• The seroprotection rate was significantly higher for influenza A than for influenza B virus (84.6% vs 37.5%; P < .001) and was higher among vaccinated than among non-vaccinated patients.
• The highest seroprotection rate and geometric mean titres were observed for subtype A(H3N2).
• Vaccinated patients had lower rates of ST-segment elevation myocardial infarction (P = .009), pulmonary embolism (P = .014), and myocarditis (P = .004) and fewer severe clinical presentations (P = .006) than non-vaccinated patients.

IN PRACTICE:

"[The study] findings reinforce the need to incorporate influenza vaccination as an integral component of inpatient management for cardiac patients during the influenza season," the authors wrote.

SOURCE:

This study was led by Alicia Galar, Hospital General Universitario Gregorio Marañón, Madrid, Spain. It was published online on January 20, 2026, in the International Journal of Infectious Diseases.

LIMITATIONS:

This study lacked pre-vaccination serum samples, so it could not determine whether measured antibodies were due to vaccination or recent infection. Defining influenza infection solely by molecular testing at admission might have missed infections in which cardiac complications occurred after viral clearance. Vaccinated and non-vaccinated groups differed substantially in age, which may have introduced confounding.

DISCLOSURES:

This study was funded by the Instituto de Salud Carlos III and co-funded by the European Union. The authors declared having no conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.