Young kids see more than 50% decline in flu-related hospitalization
• by Liz Highleyman
Contributing Writer, MedPage Today May 09, 2017
Action Points
• Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.
• The CDC estimates that children are hospitalized for influenza-related illness up to 45,000 times annually, but vaccination halved that risk.
• Overall vaccine effectiveness in preventing laboratory-¬confirmed influenza hospitalization in children was 52% for full vaccination, 46% for any vaccination, and 32% for partial vaccination.
SAN FRANCISCO — Influenza vaccines reduced the likelihood that children would be hospitalized for flu-related illness, with full vaccination providing the most protection, researchers reported here.
“Vaccination halved the risk of children being hospitalized, which was comparable to declines seen in other [community-based] studies. Overall, this was encouraging,” Angela Campbell, MD, from the CDC said here at the Pediatric Academic Societies Meeting.
Vaccines appeared to have less protective effect in older children (ages 9 to 17), but this group had more underlying conditions and other confounding factors that may have skewed their results, according to Campbell.
The CDC estimates that children in the U.S. are hospitalized with flu-related illness up to 45,000 times each year. More than half of these admissions are for young children under age 5.
Since 2008, the Advisory Committee on Immunization Practices (ACIP) has recommended yearly influenza vaccination for all children ages 6 months and older.
National estimates of influenza vaccine effectiveness in children have typically assessed protection against flu-related illness as seen by providers of outpatient care. In general, they show that vaccination reduces the risk by 50% to 60% if the virus strains chosen for the annual vaccine are similar to the actual viruses circulating during a given flu season. Less is known, however, about how well vaccination protects against more severe illness leading to hospitalization.
Campbell’s group conducted a case-control study looking at 1,542 children ages 6 months to 17 years who were hospitalized with acute respiratory illness with onset of symptoms within the past seven days.
Participants were enrolled through active surveillance at eight pediatric hospitals in the New Vaccine Surveillance Network (located in Atlanta, Cincinnati, Houston, Kansas City, Oakland, Nashville, Seattle, and Rochester, NY) during the November 2015 through June 2016 flu season.
Nasal and throat swab specimens were collected and tested for influenza and other respiratory pathogens. Within this group, 122 children (8%) tested positive for influenza. Of these, 44% had influenza type B, 41% had type A(H1N1), and 15% had type A(H3N2). The remaining 1,420 children (92%) tested negative for influenza, Campbell reported.
Vaccination status was verified using state immunization registries and provider records. Children over age 8 were considered fully vaccinated if they received at least one influenza vaccine dose. Younger children were fully vaccinated if they received two doses administered at least four weeks apart, or one dose during the current season plus one or more doses during a previous season.
Overall, 56% of children had received any flu vaccination, and two-thirds of these were considered fully vaccinated. Most (88%) received inactivated influenza vaccines, while 5% got live-attenuated vaccines.
The vaccine effectiveness analysis showed that children with influenza were less likely to have been vaccinated. Across all age groups, 39% of influenza-positive children had received any vaccination, compared with 57% in the influenza-negative group; 29% and 47%, respectively, were considered fully vaccinated.
After adjusting for potential confounding factors including age and underlying conditions, overall vaccine effectiveness was 52% for full vaccination, 46% for any vaccination, and 32% for partial vaccination, Campbell reported.
“Vaccine effectiveness for partially vaccinated children was much lower and not significant,” she said.
When the results were broken down by age, adjusted vaccine effectiveness for any vaccination was 65% for babies ages 6 to 23 months and 51% for children ages 2 to 8 years, but fell to just 29% for older children and adolescents ages 9-17 years.
“The estimate for the 9-17 age group was extremely low, but it had a large confidence interval and they had more underlying conditions,” Campbell said.
Joshua Wolf, MBBS, from St. Jude Children’s Research Hospital, who moderated the session, urged caution with regard to the older age group in this study.
“There are some limitations related to the study design, such as using controls with respiratory infection rather than community patients, that make me especially cautious about interpretation of the data for older children and teenagers, where the vaccine appeared less effective. I suspect that this is related to confounding — more analysis is needed to assess this,” he told MedPage Today.
Despite this reservation, Campbell’s group concluded, “Our study provides important data to support the use of influenza vaccination to prevent severe illness in children.”