Study shows safety of flu vaccination for hospitalized patients

Hospitalized patients who received the flu vaccine had no increased risk of outpatient visits or hospital readmission within seven days of discharge, according to a Kaiser Permanente study published today in Mayo Clinic Proceedings.

The study also showed that vaccinating hospital patients did not increase the risk of fever or rates of laboratory evaluations for infection. It also showed that the vast majority of patients who were not vaccinated during their hospital stay remained unvaccinated for the full flu season.

"We know rates of inpatient flu vaccination are low, often due to physician concerns that the vaccine could complicate healing or delay hospital discharge," said Sara Y. Tartof, PhD, MPH, study lead author, Kaiser Permanente Southern California Department of Research & Evaluation. "Our findings demonstrate that not vaccinating patients during a hospitalization may be a missed opportunity. Right now, only 28 percent of patients not already vaccinated prior to hospitalization are being vaccinated before they leave the hospital."

This study builds upon previous research that showed surgical patients who received the flu vaccine during their hospital stay did not have increased risks of complications or delay in discharge compared to surgical patients who were not vaccinated during their stay.

The flu is a highly contagious respiratory infection that can cause serious complications, hospitalizations and, in some cases, even death. Some people -- such as older adults, young children and people with certain health conditions -- are at high risk for serious complications if they get the flu. In addition to recommending annual flu vaccination for people ages 6 months and older, the Centers for Disease Control and Prevention recommends hospitalized patients who are eligible receive the flu vaccine before discharge.

This retrospective cohort study looked at the electronic health records of more than 250,000 patients ages 6 months and older who were hospitalized in a Kaiser Permanente hospital in Southern California during any of three flu seasons from 2011 to 2014 with admission and discharge dates between September 1 and March 31 of the following calendar year.

Researchers found:

• 71 percent of patients vaccinated during their hospital stay were vaccinated on the day of discharge.
• 74 percent of those who miss the opportunity to vaccinate before or during hospitalization remained unvaccinated throughout the season.
• No increased risk of hospital readmissions, outpatient visits, fever, or clinical evaluations for infection among patients who received the flu vaccine during their hospital stay.

"This research backs up what many physicians have known intuitively for some time: Giving patients the flu vaccine while they are hospitalized is convenient and, most important, safe," said Bruno J. Lewin, MD, a family practice physician at the Kaiser Permanente Los Angeles Medical Center. "Unless there are contraindications, physicians should have no hesitation to vaccinate patients with the flu vaccine while they are hospitalized."