By Lisa Rapaport

(Reuters Health) – Patients who receive the flu vaccine while hospitalized are no more likely to develop fever or require extra doctor or hospital visits after they go home than inpatients who don’t get vaccinated, a large study suggests.

Even though most people in the U.S. are advised to get an annual flu shot, many don’t do it consistently, researchers note in the Mayo Clinic Proceedings. Doctors are often reluctant to vaccinate hospitalized patients out of concern that doing so might lead to complications that require extra care or cause needless stress.

For the current study, researchers examined data on 290,149 U.S. hospitalizations involving 255,737 patients over three consecutive flu seasons. Almost half of the patients had been vaccinated before they got to the hospital, while nearly 16 percent received the flu vaccine during their stay. Another 27 percent never got vaccinated, and the rest got a flu vaccination at some point after they were discharged from the hospital.

Researchers found no meaningful differences in the risk of fevers, repeat hospitalizations, checkups for infections, or outpatient visits during the first week after discharge between people who got vaccinated during their hospital day and those who did so at other times or never got vaccinated.

“When someone is hospitalized, that means that they are in a very vulnerable health situation,” said lead study author Sara Tartof of Kaiser Permanente Southern California in Pasadena.

“Clinicians may not want to vaccinate at this time due to concerns that it could complicate care, or make a very sick patient feel even worse,” Tartof said by email. “However, we did not find this to be the case.”

The U.S. Centers for Disease Control and Prevention (CDC) recommends a yearly flu vaccine for virtually everyone aged 6 months and older, ideally by the end of October. But roughly half of Americans don’t consistently follow this advice.

Only 28 percent of the patients in the study who had not been vaccinated before entering the hospital received the vaccine during their stay. And only 26 percent of those who left the hospital unvaccinated received the vaccine during that season.

The study wasn’t designed to prove whether or how the timing of vaccination might directly influence complications like fever or repeat hospitalizations. The study is also limited by the fact that researchers didn’t distinguish between planned and unplanned doctor visits or hospital stays within the first week after discharge.

Still, the results should reassure doctors and patients that it’s safe to get the flu vaccine during a hospital stay, said Dr. Kevin Schwartz, a researcher at Public Health Ontario and the University of Toronto who wasn’t involved in the study.

“There are many studies showing that the yearly flu shot is safe and well tolerated by most patients, even those with significant medical problems,” Schwartz said by email.

“Everyone is encouraged to get a flu shot every year in the fall before flu season as the most effective tool to prevent influenza and its associated complications for yourself and those around you,” Schwartz added. “This study is a nice reminder that patients who get admitted to hospital who are unvaccinated during flu season can be safely vaccinated before discharge.”

SOURCE: Mayo Clinic Proceedings, online January 8, 2019.