WASHINGTON — Influenza vaccination reduced the risk for influenza-related hospitalization in children by nearly half and the odds of death in adults by about 36% over several recent influenza seasons, according to CDC data from two studies presented at IDWeek.
In the first study, Angela P. Campbell, MD, MPH, a medical officer in the CDC’s Influenza Division, and colleagues assessed influenza vaccine effectiveness in preventing influenza-related hospitalizations among 3,441 children younger than age 18 years with acute respiratory illness who were enrolled at seven pediatric hospitals in the New Vaccine Surveillance Network.
“We at CDC have performed studies of vaccine effectiveness for years but most have been in the outpatient network,” Campbell told Infectious Disease News. “We recently restarted a collaboration with the New Vaccine Surveillance Network, which is a network of academic sites that allows us to look at inpatient estimates and at how well the vaccine works against more severe disease and outcomes including hospitalization.”
Data presented showed that during the 2016-2017 season, 163 of 1,714 children (10%) tested positive for influenza — 56% with influenza A(H3N2), 4% with A(H1N1) and 39% with B viruses. During the 2017-2018 season, 218 of 1,916 (11%) children tested positive — 40% with influenza A(H3N2), 24% with A(H1N1) and 33% with B viruses.
According to the findings, in 2016-2017, influenza vaccine effectiveness for all vaccinated children was 49% (95% CI, 26%-63%). It was 51% (95% CI, 24%-60%) in 2017-2018. Combined, the vaccine effectiveness was 50% (95% CI, 32%-58%) in the two seasons.
“This gives us even more evidence to support the recommendation that all children and adults should get a flu vaccination every year,” Campbell said. “It really highlights the importance for protection against more severe disease but also goes back to the recommendation that the best way to prevent any flu, including severe flu, is vaccination.”
A second study by Shikha Garg, MD, MPH, a medical epidemiologist at the CDC, and colleagues compared the severity of influenza outcomes among 43,608 vaccinated and unvaccinated adults aged 18 years or older who were hospitalized with influenza during five influenza seasons starting with 2013-2014 in more than 250 acute care hospitals in 13 states.
“Every year millions of people get the flu. Hundreds of thousands are hospitalized, and thousands to tens of thousands die because of flu,” Garg said during a news conference. “There’s a general thought that vaccination reduces the severity of illness in those who get sick but there haven’t really been many studies and the studies that have looked at this have had mixed results.”
Study participants were identified through the U.S. Influenza Hospitalization Surveillance Network. Data showed that for adults with influenza A(H1N1), vaccination was associated with decreased odds of ICU admission in adults aged 18 to 64 (OR = 0.81) and adults aged 65 or older (OR = 0.72). Vaccination also was associated with decreased odds of mechanical ventilation in adults aged 18 to 64 (OR = 0.66) and adults aged 65 or older (OR = 0.54) Additionally, vaccination decreased the odds of pneumonia by 17% (OR = 0.83) and death by 36% (OR = 0.64) and shortened ICU length of stay (relative hazard [RH] = 0.82) in adults 18 to 64 years and shortened hospital length of stay (RH = 0.91) in adults 65 or older.
“The takeaway is that while vaccines vary in how they work and some people who get vaccinated still get sick, this study provides more evidence that getting vaccinated reduces severity of illness,” Garg said. – by Caitlyn Stulpin
Disclosures: Campbell and Garg report no relevant financial disclosures.
Campbell AP, et al. Abstract 899. Presented at: IDWeek; Oct. 2-6, 2019; Washington.
Garg S, et al. Abstract 898. Presented at: IDWeek; Oct. 2-6, 2019; Washington.