TOPLINE:

Seasonal influenza vaccination was associated with a reduced risk for progression to lower respiratory tract disease and hospitalisation in allogeneic haematopoietic stem cell transplant (allo-HCT) recipients with laboratory-confirmed influenza infection.

METHODOLOGY:

• Researchers in Spain conducted a multicentre retrospective study to assess whether seasonal inactivated influenza vaccination reduces the severity of influenza infection in allo-HCT recipients with laboratory-confirmed influenza infection.
• They analysed 143 allo-HCT recipients (median age, 45 years; 57% men) who experienced 214 laboratory-confirmed influenza infection episodes between December 2013 and June 2023.
• Recipients were categorised as vaccinated if a trivalent or quadrivalent inactivated influenza vaccine was administered before the onset of infection during the same season, unvaccinated if they did not receive the vaccine during that season, and vaccination ineligible if influenza infection occurred within 90 days after transplant.
• The primary objective was to analyse the effect of vaccination on the risk for progression to lower respiratory tract disease and to identify other potential associated factors; secondary outcomes included the need for hospitalisation and oxygen supplementation.

TAKEAWAY:

• Overall, 22% of episodes occurred after seasonal influenza vaccination; the median time from allo-HCT to infection was 427 days, and 29% of episodes progressed to lower respiratory tract disease.
• Influenza vaccination was independently associated with an 81% reduced risk for progression to lower respiratory tract disease (adjusted hazard ratio [aHR], 0.19; P = .001) and 82% lower odds of hospitalisation (adjusted odds ratio, 0.18; P = .005).
• A high-risk immunodeficiency scoring index (aHR, 4.77; P = .0004) and fever at the time of influenza diagnosis (aHR, 4.49; P < .001) were independently associated with an increased risk for progression to lower respiratory tract disease.
• Moderate-risk and high-risk immunodeficiency scoring index categories, as well as high-dose (≥ 30 mg/d) corticosteroid use, were independent risk factors for hospitalisation and the need for oxygen supplementation.

IN PRACTICE:

"Our results support considering influenza vaccination at any time after transplant during influenza season and highlight the need to assess its potential clinical effectiveness in this patient subset through prospective clinical trials," the authors wrote.

SOURCE:

This study was led by Clara Isabel Martínez-López, Hospital Clínico Universitario de Valencia, Valencia, Spain. It was published online on December 31, 2025, in Open Forum Infectious Diseases.

LIMITATIONS:

This study was retrospective, with a relatively small sample size, and vaccination policies varied over time. Differences in sensitivity and specificity of laboratory tests could have affected virus detection. The exact timing of progression from upper to lower respiratory tract disease could not be accurately determined.

DISCLOSURES:

This study did not receive any funding, and 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.