Adults hospitalized for pneumonia who received influenza vaccination during their stay were less likely to seroconvert if they had diabetes, bacterial detection, baseline seropositive titers for influenza B, or influenza vaccination in the previous season, according to study results published in the journal Influenza and Other Respiratory Viruses .
Whole blood samples from adults hospitalized with radiographically confirmed community acquired pneumonia and negative testing for influenza were evaluated for antibody titers following influenza vaccination. A patient was considered to have seroconverted if a ≥4-fold rise in hemagglutination inhibition antibody titers occurred. Seropositive titers were defined as hemagglutination inhibition ≥1: 40. Patient health variables were then evaluated to determine which variables may be associated with nonseroconversion.
Of the 2320 adults screened, 95 met the inclusion criteria and were included in the analysis. Patients who did not seroconvert were more likely to have diabetes mellitus and a baseline hemagglutination inhibition ≥40 for influenza B compared with patients who seroconverted. Age, immunosuppression, pneumonia severity index score, intensive care unit admission, and duration of hospitalization did not differ between patients who seroconverted and patients who did not.
Multivariable logistic regression model
In the final multivariable logistic regression model, only diabetes, previous seasonal influenza vaccine, bacterial pathogen detection, and baseline seropositive titers to influenza B (Yamagata) were significantly associated with nonseroconversion. A total of 66 patients seroconverted to ≥1 influenza virus strain.
The investigators wrote, "We had anticipated that age, mild immunosuppression, or measures of [community-acquired pneumonia] severity (eg, [pneumonia severity index] score, duration of hospitalization, and ICU [intensive care unit] admission) might explain differences in seroconversion, but these associations were not observed. " They added, "Identifying adults at risk for seroconverting with standard influenza vaccination could focus future prospective clinical trials of new influenza vaccination strategies."