Field seasonal influenza vaccine effectiveness

Effectiveness of 2012–2013 influenza vaccine against influenza-like illness in general population

“…5 Although we did not observe a significant effect of the vaccination in at-risk population, probably because of a lack of statistical power, we can observe a tendency to have a lower IVE in the overall population (32%, 0 to 58), especially for individuals over 65 yo (28%, 0 to 61), which is inline with literature findings. 4,[19][20][21][22][23][24][25] No significant effect of the vaccination (P = 0.63) was found outside influenza viral circulation, thus strengthening the validity of our results.…”

“…This evaluation is a complex problem to address, because of confounding factors and biases linked to the design of the observational studies (case-control study, cohort study, screening method), the sensitivity and specificity of the case definition used (influenza-like illness or virologically confirmed influenza), the case report system, the differences in risk exposure between vaccinated and unvaccinated individuals, and the targeted population. [2][3][4] Because of practical issues, studies of IVE have used a variety of non-specific outcome measures rather than virological-proven influenza, including the prevention of acute respiratory illness (ARI), influenza-like illness (ILI), pneumonia-associated hospitalizations or deaths. [5][6][7] Today, most of these observational studies are based on a population of patients consulting a general practitioner (GP) for ILI, which is not a randomized ILI sample, 8 as the majority of individuals with an ILI do not systematically access the healthcare systems.…”