The New England Journal of Medicine did a study on the efficacy of a vaccine for the
influenza A virus. A total of 1,952 subjects were enrolled and received study vaccines in the fall of 2007. Influenza activity occurred from January through April 2008, with the circulation of influenza types:
- A (H3N2) (about 90%)
- B (about 9%)
Absolute efficacy against both types of influenza, as measured by isolating the
virus in culture, identifying it on real-time
polymerase-chain-reaction assay, or both, was 68% (95%
confidence interval [CI], 46 to 81) for the
inactivated vaccine and 36% (95% CI, 0 to 59) for the
live attenuated vaccine. In terms of relative efficacy, there was a 50% (95% CI, 20 to 69) reduction in laboratory-confirmed influenza among subjects who received inactivated vaccine as compared with those given live attenuated vaccine. Subjects were healthy adults. The efficacy against the influenza A virus was 72% and for the inactivated was 29% with a relative efficacy of 60%.
[21] The
influenza vaccine is not 100% efficacious in preventing disease, but it is close to 100% safe, and much safer than the disease.
[22][23]
Since 2004, clinical trials testing the efficacy of the influenza vaccine have been slowly coming in: 2,058 people were vaccinated in October and November 2005. Influenza activity was prolonged but of low intensity; type A (H3N2) was the virus that was generally spreading around the population, which was very like the vaccine itself. The efficacy of the inactivated vaccine was 16% (95% confidence interval [CI], -171% to 70%) for the virus identification end point (virus isolation in cell culture or identification through polymerase chain reaction) and 54% (95% CI, 4%–77%) for the primary end point (virus isolation or increase in
serum antibody titer). The absolute efficacies of the live attenuated vaccine for these end points were 8% (95% CI, -194% to 67%) and 43% (95% CI, -15% to 71%).
[24]