CDC Analyses Show Flu Vaccine Reduces Risk of Hospitalization in Children and Death in Adults

Two analyses by the Centers for Disease Control and Prevention (CDC) show the influenza (flu) vaccine can reduce the likelihood of hospitalization in children and death in adults.

In the first study, conducted by seven pediatric medical centers comprising the New Vaccine Surveillance Network, researchers analyzed flu test results from 3,600 children aged 6 months to 17 years who were hospitalized with acute respiratory illness over two seasons in which influenza A(H3N2) viruses were the predominantly circulating virus. Patients were tested for influenza using molecular diagnostic tests, which found 163 out of 1,714 (10 percent) during the 2016-2017 season and 218 out of 1,916 (11 percent) during the 2017- 2018 season tested positive for flu, including A(H3N2), A(H1N1) and B viruses. They then estimated how well the flu vaccine worked to reduce hospitalizations due to laboratory-confirmed influenza by comparing the frequency of flu vaccination among children who tested positive for flu to vaccination among children without flu, adjusting for age, race/ethnicity, enrollment month, study site and underlying medical conditions. Based on this information, the vaccine effectiveness against influenza-associated hospitalizations was 50 percent over the two seasons (49 percent for the first season and 51 percent the second), meaning vaccination reduced the risk of hospitalization with flu by about half.

In the second study, researchers looked at five flu seasons using the U.S. Influenza Hospitalization Surveillance Network and identified 43,608 adults (18 and older) hospitalized with laboratory-confirmed flu. Overall, 38 percent of those 18 years to 64 years old and 65 percent of those 65 years or older had received a flu vaccine. Researchers assessed vaccination status among hospitalized patients to determine the reduction in the odds of severe outcomes among vaccinated patients compared to those who were unvaccinated. Findings showed that in patients diagnosed with influenza A(H1N1), flu vaccination reduced their odds of severe outcomes, including death (36 percent), pneumonia (17 percent), intensive care unit (ICU) (19 percent) and mechanical ventilation (34 percent). Vaccination also was associated with a shorter ICU length of stay. And, in those 65 years or older, flu vaccination was associated with reduced risk of ICU admission (28 percent) and mechanical ventilation (46 percent).

“These studies add to the evidence that influenza vaccines prevent serious complications from flu,” said Angela P. Campbell, MD, MPH, FIDSA, FPIDS, lead author of the study in children and medical officer in the epidemiology and prevention branch of the influenza division at CDC. “They show just how important it is that everyone 6 months and older who is eligible to get a flu vaccine does so every year.”