Studies Show Flu Vaccine Reduces Risk of Hospitalization in Children and Death in Adults:
National Flu Surveillance Research
AT A GLANCE
WASHINGTON, D.C. – The influenza (flu) vaccine can not only prevent illness that may cause a week or more of misery, it can reduce the likelihood of hospitalization in children and death in adults, according to two analyses of Centers for Disease Control and Prevention (CDC)-supported U.S. influenza surveillance data being presented at IDWeek 2019.
The first study supports the benefit of flu vaccination in preventing severe outcomes in children. Children who received the influenza vaccine were half as likely to be hospitalized with flu as those who didn’t get vaccinated, according to the study, which followed more than 3,600 children over two seasons.
The second study looked at more than 43,000 older adults hospitalized with flu over five seasons and found that vaccination reduced the risk of severe outcomes – including death, pneumonia, intensive care admission and mechanical ventilation – by more than one-third.
“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 the CDC, Atlanta. “They show just how important it is that everyone six months and older who is eligible to get a flu vaccine does so every year.”
Flu vaccination in children reduces risk of hospitalization
In the first study, conducted by seven pediatric medical centers comprising the New Vaccine Surveillance Network, researchers analyzed flu test results from 3,630 children, aged 6 months to 17 years old, who were hospitalized with acute respiratory illness over two flu seasons in which influenza A(H3N2) viruses were the predominantly circulating virus. Patients were tested for influenza using molecular diagnostic tests: 163 out of 1,714 (10%) during the 2016-2017 season and 218 out of 1,916 (11%) during the 2017-2018 season tested positive for flu, including A(H3N2), A(H1N1) and B viruses.
Researchers 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% over the two seasons (49% for the first season and 51% the second), meaning that vaccination reduced the risk of hospitalization with flu by about half.
“This is encouraging given that flu vaccines often work better against H1N1 and B flu viruses than against H3N2 viruses,” said Dr. Campbell. “Our findings support the use of vaccination to prevent severe flu illness in children during every flu season, regardless of which viruses are predominant.”
Flu vaccination in adults reduces risk of death
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% of those 18 to 64 years old and 65% of those 65 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. The findings showed that in patients diagnosed with influenza A(H1N1), flu vaccination reduced their odds of severe outcomes, including death, by 36%. Severe outcomes included death, pneumonia, admission to the intensive care unit and mechanical ventilation.
Flu vaccination in adults 18-64 with A/(H1N1) influenza was associated with reduced risk of the following: 36% death, 17% pneumonia, 19% intensive care unit (ICU) admission and 34% mechanical ventilation. Vaccination also was associated with a shorter ICU length of stay. Flu vaccination in those 65 years or older was associated with reduced risk of the following: 28% ICU admission, 46% mechanical ventilation. It was also associated with a shorter hospital length of stay.
“While flu vaccines vary in how well they work and some people who get vaccinated still get sick, this study provides more evidence that getting vaccinated can reduce the severity of the illness,” said Shikha Garg, MD, MPH, lead author of the study and a medical officer in the Epidemiology and Prevention Branch of the Influenza Division at the CDC. “This type of research helps us more fully understand the benefits of vaccination.”
In addition to Dr. Campbell, co-authors of the study in children are: Constance E. Ogokeh, MPH, Craig McGowan, MS, Brian Rha, MD, MSPH, Rangaraj Selvarangan, BVSc, PhD, FIDSA, Mary A. Staat, MD, MPH, Geoffrey A. Weinberg, MD, FPIDS, Julie A. Boom, MD, Janet A. Englund, MD, FPIDS, John V. Williams, MD, Natasha B. Halasa, MD, MPH, FPIDS, Peter G. Szilagyi, MD, MPH, Christopher J. Harrison, MD, FPIDS, Eileen J. Klein, MD, MPH, Monica McNeal, MS, Marian G. Michaels, MD, MPH, Leila C. Sahni, PhD, MPH, Laura S. Steward, PhD, Joana Y. Lively, MPH, Lauren Beacham, MA, Daniel C. Payne, PhD, MSPH, Alicia M. Fry, MD, MPH and Manish Patel, MD.
In addition to Dr. Garg, co-authors of the study in adults are: Lauren Beacham, MA, Carmen S. Arriola, DVM, PhD, Alissa O’Halloran, MSPH, Charisse N. Cummings, MPH, Art Reingold, MD, FIDSA, Nisha B. Alden, MPH, Kim Yousey-Hindes, MPH, CPH, Evan J. Anderson, MD, Maya Monroe, MPH, BS, Sue Kim, BS, MPH, Ruth Lynfield, MD, FIDSA, Lourdes Irizarry, MD, Alison Muse, MPH, Nancy M. Bennett, MD, MS, Laurie M. Billing, MPH, Ann Thomas, MD, Keipp Talbot, MD, MPH, FIDSA, Keegan McCaffrey, BA, Alicia M. Fry, MD, MPH and Carrie Reed, DSc, MPH.
IDWeek 2019TM is the annual meeting of the Infectious Diseases Society of America (IDSA), the Society for Healthcare Epidemiology of America (SHEA), the HIV Medicine Association (HIVMA) and the Pediatric Infectious Diseases Society (PIDS). With the theme “Advancing Science, Improving Care,” IDWeek features the latest science and bench-to-bedside approaches in prevention, diagnosis, treatment, and epidemiology of infectious diseases, including HIV, across the lifespan. IDWeek 2019 takes place Oct. 2-6 at the Walter E. Washington Convention Center in Washington, D.C. For more information, visit www.idweek.org.