Safety of Influenza Vaccination Administered During Hospitalization

To determine whether influenza vaccination during hospitalization increases health care utilization, fever, and infection evaluations postdischarge.

This retrospective cohort study conducted at Kaiser Permanente Southern California included patients aged 6 months or older hospitalized in a Kaiser Permanente Southern California facility with admission and discharge dates between September 1 and March 31 of the following calendar year, from 2011 to 2014. All influenza vaccinations administered during the period of August 1 to April 30 for influenza seasons 2011-2012, 2012-2013, and 2013-2014 were identified. We compared the risk of outcomes of interest between those who received influenza vaccination during their hospitalization vs those who were never vaccinated that season or were vaccinated at other times using propensity score analyses with inverse probability of treatment weighting. Outcomes of interest included rates of outpatient and emergency department visits, readmissions, fever, and clinical laboratory evaluations for infection (urine, blood, and wound culture; complete blood cell count) in the 7 days following discharge.

We included in the study 290,149 hospitalizations among 255,737 patients. In adjusted analyses, we found no increased risk of readmissions (relative risk [RR], 0.88; 95% CI, 0.83-0.95), outpatient visits (RR, 0.97; 95% CI, 0.95-0.99), fever (RR, 0.80; 95% CI, 0.68-0.93), and clinical evaluations for infection (RR, 0.95; 95% CI, 0.92-0.98) among those vaccinated during hospitalization compared with those who were never vaccinated or were vaccinated at other times.

Our findings provide reassurance about the safety of influenza vaccination during hospitalization. Every contact with a health care professional, including during a hospitalization, is an opportunity to vaccinate.