Question explored with the scientific record
fluenz
Fluenz is a live, weakened flu vaccine sprayed up the nose. In children it beats the shot on protection, but it carries a real wheezing signal in the youngest kids.
The evidence here is pediatric and mostly company-funded. The strongest head-to-head trial, in children with recurrent chest infections, was paid for by Wyeth and MedImmune, the makers [3]. It found the nasal spray cut confirmed flu 53% better than the shot against matched strains, but showed no benefit against the H3N2 strain [3]. A review reports the same pattern: nasal spray beat the shot by 35-53% in children, with high efficacy against matched strains [4]. In adults the picture is weaker, and effectiveness was not shown in the 50-64 group [4].
The safety signal is real and age-specific. In children 6-23 months, medically significant wheezing was higher with the spray than the shot, about 6 in 100 versus 4 in 100 [4]. That is why it is not used in the youngest children. In older high-risk kids with asthma, a large English cohort found no significant rise in hospitalization after the spray [1], and a small placebo-controlled trial in asthmatic children found no lung-function drop [2]. But that trial had only 24 kids per group [2].
| Group | Finding | Source |
|---|---|---|
| Kids 6-71 months, vs shot | 53% better against matched flu | [3] |
| Kids 6-71 months, H3N2 | No significant benefit | [3] |
| Kids 6-23 months | Wheezing 5.9% vs 3.8% | [4] |
| Asthmatic kids, hospitalization | No significant increase | [1] |
What this retrieval cannot see: long-term safety, and any trial comparing vaccinated children to truly unvaccinated ones over years. Those were not here.
My call: for a healthy child over 2, the nasal spray is a reasonable option and beats the shot on matched flu; for a child under 2 or with poorly controlled asthma, the wheezing signal argues against it. Confidence: moderate.
Sources used 4
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Evaluation of the safety of live attenuated influenza vaccine (LAIV) in children and adolescents with asthma and high-risk conditions: a population-based prospective cohort study conducted in England with the Clinical Practice Research Datalink
In a prospective CPRD cohort matching 11,463 children and adolescents with asthma or other high-risk conditions, LAIV was not significantly associated with higher hospitalisation than no vaccination, and hospitalisation rates were lower after LAIV than after IIV.
DOI: 10.1136/bmjopen-2018-023118 -
Safety and tolerability of cold-adapted influenza virus vaccine in children and adolescents with asthma
A randomized, double-blind, placebo-controlled trial assessing the safety and tolerability of intranasal live attenuated CAIV-T influenza vaccine in children and adolescents with moderate to severe asthma, finding no significant adverse effects on lung function or exacerbations …
DOI: 10.1097/00006454-200201000-00010 -
Superior Relative Efficacy of Live Attenuated Influenza Vaccine Compared With Inactivated Influenza Vaccine in Young Children With Recurrent Respiratory Tract Infections
A multicenter, randomized phase III trial in 6- to 71-month-old children with recurrent respiratory tract infections shows that cold-adapted influenza vaccine, trivalent (CAIV-T) provides superior protection against culture-confirmed influenza strains antigenically similar to th…
DOI: 10.1097/01.inf.0000237829.66310.85 -
Current status of live attenuated influenza vaccine in the United States for seasonal and pandemic influenza
Live attenuated influenza vaccine showed high efficacy against matched and mismatched influenza strains in children and provided significant but less consistent protection in adults, with a wheezing safety signal in the youngest children and pandemic candidates in early developm…
DOI: 10.1111/j.1750-2659.2008.00056.x