What does the term "vaccine efficacy" refer to?

The term "vaccine efficacy" specifically refers to the percentage reduction of disease incidence among vaccinated individuals compared to those who are unvaccinated in a controlled clinical trial setting. This metric provides a quantitative measure of how well a vaccine performs in preventing the targeted disease under ideal conditions.

When evaluating a new vaccine, researchers conduct clinical trials to determine how well it works. They compare the incidence of the disease between the vaccinated group and the unvaccinated group. If a vaccine is shown to significantly lower the occurrence of the disease in the vaccinated population, this reduction is expressed as vaccine efficacy. For instance, if a vaccine has 90% efficacy, it means that vaccinated individuals have a 90% lower risk of contracting the disease compared to those who are not vaccinated.

Understanding vaccine efficacy is essential for public health, as it informs health policies, vaccination recommendations, and the overall assessment of a vaccine's potential impact on disease control and prevention. This measurement helps determine how beneficial a vaccine is, thereby guiding decisions on its use and distribution in the general population.