How effective are vaccines in preventing influenza in healthy adults (aged between 16 and 65 years)?
These results may be an optimistic estimate because companysponsored influenza vaccines trials tend to produce results favourable to their products, and some of the evidence came from trials carried out in ideal viral circulation and matching conditions; also because the harms evidence base was limited. Fifteen of the 36 trials in the review were funded by vaccine companies and 4 had no funding declaration.
Over 200 viruses cause influenza and influenza-like illness (which produces the same symptoms). At best, vaccines might be effective against only influenza A and B, which represent about 10% of all circulating viruses. Healthy adults are presently targeted for influenza vaccination mainly in North America.