Influenza Vaccine Keeps Kids Out of Intensive Care, CDC Says

Larry Hand

March 28, 2014

Children who are fully vaccinated against influenza may have a 74% reduced risk of developing life-threatening influenza illness compared with unvaccinated children, according to a study published online March 26 in the Journal of Infectious Diseases.

Jill M. Ferdinands, PhD, from the Centers for Disease Control and Prevention, Atlanta, Georgia, and colleagues conducted a case-control study comparing medical records of confirmed influenza cases with 2 different control groups during the 2010-2011 and 2011-2012 influenza seasons.

The study involved 216 children aged between 6 months and 17 years admitted to 21 US pediatric intensive care units (PICUs). Of those children, 44 were admitted to PICUs and tested positive for influenza and 172 (PICU control patients) were admitted but did not test positive. An additional 93 (community control participants) children were recruited from surrounding areas and matched to case patients by comorbidities and geography.

The researchers classified the children as fully or partially vaccinated on the basis of recommendations of the US Advisory Committee on Immunization Practices. They obtained the vaccination status of the children from a combination of parental reports and a review of medical records and immunization registries.

Low Vaccination Rates

The researchers found that only 62 (29%) of the 216 PICU-admitted children were fully vaccinated and 34 (16%) were partially vaccinated. For the 44 influenza-confirmed cases, only 8 (18%) were fully vaccinated, 6 (14%) were partially vaccinated, and 30 (68%) were not vaccinated. In comparison, 54 (31%) of PICU control patients were fully vaccinated, 28 (16%) were partially vaccinated, and 90 (52%) were not vaccinated. For the community control patients, 47 (51%) were fully vaccinated per parental report.

When the researchers compared vaccine effectiveness for case patients and PICU control patients, they estimated that the adjusted effectiveness for full influenza vaccination for preventing PICU admission was 74% (95% confidence interval [CI], 19% - 91%; P = .02) compared with no vaccination. For case patients compared with community control participants, adjusted effectiveness was 82% (95% CI, 23% - 96%; P = .02). They found no effectiveness for partial vaccination.

The researchers used logistic regression modeling to compare cases with PICU control patients, adjusting for variables including age, sex, and time of illness onset, as well as geographic area. Modeling to compare cases to community controls included race, which was not a confounder in the other analysis.

"To our knowledge, this study is the first to specifically estimate [vaccine effectiveness] against life-threatening outcomes of influenza infection in children," the researchers write. The CDC's usual measure for vaccine effectiveness is how well it protects against having to see a physician for influenza symptoms, according to a CDC news release.

Although the researchers conducted the study beginning a year after the 2009 influenza pandemic, during a period of "heightened awareness," the results showed low vaccination coverage. "[L]ess than a third of cases and PICU controls were fully vaccinated, even though almost half of these had at least one high risk condition," the researchers write.

"These study results underscore the importance of an annual flu vaccination, which can keep your child from ending up in the intensive care unit," Alicia Fry, MD, MPH, a medical officer in the CDC's Influenza Division, said in a CDC news release. "It is extremely important that all children — especially children at high risk of flu complications — are protected from what can be a life-threatening illness."

This research was supported by funding from the CDC to Abt Associates, Cambridge, Massachusetts. Dr. Ferdinands has reported she has received travel support from Sanofi for an unrelated project. The other authors and Dr. Fry have disclosed no relevant financial relationships.

J Infect Dis. Published online March 26, 2014. Full text

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