- Inactivated quadrivalent influenza vaccine (IIV4) attenuates influenza severity in breakthrough cases among young children ages 6-35 months without high-risk conditions.
- Clinical symptoms alone do not distinguish influenza from other common respiratory illnesses.
Why this matters
- Data further confirm value of offering/encouraging annual influenza vaccination to young children, including those without conditions that increase risk for severity.
- Timely diagnosis with available diagnostic tests is essential to avert hospitalization.
- 12,018 children; median age, 22 months.
- 6625 influenza-like illness episodes; 987 confirmed positive by reverse transcription PCR (RT-PCR); 5464 were RT-PCR-negative.
- 356 IIV4-vaccinated children and 693 controls had RT-PCR-confirmed influenza.
- Moderate-to-severe illness was 41% less common with IIV4 vaccination (crude OR=0.59; 95% CI, 0.44-0.77).
- Symptom frequency/duration was similar in both groups except for a lower prevalence of fever >39 ºC in IIV4-vaccinated children (17.7% [95% CI, 13.8%-22.1%] vs 28.30% [95% CI, 25.0%-31.9%]).
- Crude OR=0.54; 95% CI, 0.39-0.75.
- IIV4-vaccinated children had lower odds of breakthrough influenza (crude OR=0.59; 95% CI, 0.44-0.77).
- Exploratory analysis of phase 3, multicenter trial data to assess influenza clinical presentation in children ages 6-35 months without risk factors, effect of IIV4 vaccination on outcomes.
- Funding: GlaxoSmithKline.
- True vaccine effect underestimated.
- Seasonal strains variations, population susceptibility to circulating strains unmeasured.