Live attenuated vaccine less effective in recent influenza season

1. Live attenuated influenza vaccine (LAIV), administered intranasally, was less effective in recent seasons at preventing influenza A/H1N1pdm09 among children and adolescents than the intramuscularly-administered inactivated version (IIV).

Study Rundown: Though prior studies had supported use of intranasal LAIV, there is little data to compare its effectiveness against the traditional, intramuscular IIV since the 2009 H1N1 pandemic. In light of this lack of information, researchers in the current study sought to compare vaccine effectiveness among recipients vaccinated with LAIV or IIV. Researchers examined influenza infection rates in vaccinated participants aged 2 years to 17 years from 2010 to 2014. In this large, observational study, LAIV was found to be less effective than IIV in preventing A/H1N1pdm09 influenza in children and adolescents during the 2010-2011 and 2013-2014 seasons, with no significant differences seen in vaccine effectiveness against influenza A/H3N2 or B. This study was limited by its observational study design and small sample size. Despite these concerns, findings should encourage pediatricians to be cautious in utilizing LAIV in the clinical setting while noting varying yearly vaccine formulations.

Click to read the study, published today in Pediatrics

Relevant Reading: Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices (ACIP)

In-Depth [observational study]: A total of 2703 individuals, aged 2 to 17 years, seeking acute respiratory care in the outpatient setting, were included in this study. Nasal and throat swabs were collected to test for influenza status, which was subsequently confirmed via polymerase chain reaction, also known as PCR. Vaccination status was confirmed via electronic medical record, registry data or parental/guardian report. Among vaccinated participants, 76.4% received IIV (n = 2066) whereas 23.6% received LAIV (n = 637). When compared by season, odds of influenza in LAIV and IIV recipients in 2010-2013 were similar, with no statistically significant difference in vaccine effectiveness. However, in 2013-2014, the odds of influenza in LAIV recipients aged 2 to 17 years was significantly higher than those who received IIV (OR 2.88; 95%CI 1.62-5.12) as well as for recipients aged 2 to 8 years (OR 5.36; 95%CI 2.37-12.13). When compared by influenza type, the odds of illness with influenza A/H3N2 or B were similar for participants vaccinated with LAIV or IIV. However, the odds of influenza A/H1N1pdm09 positivity among LAIV recipients aged 2 to 17 years were 5.53 times higher in 2010-2011 (95%CI 1.35-22.76) and 2.65 times higher in 2013-2014 (95%CI 1.34-5.27) compared with IIV recipients.

Image: PD

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