Efficacy of vaccines

Vaccine efficacy refers to how well a vaccine prevents a disease in controlled studies. For example, if a vaccine has 90% efficacy, it means that vaccinated individuals are 90% less likely to get the disease compared to those who are unvaccinated. It measures the relative reduction in risk, not absolute protection, and varies depending on factors like the disease, population, and circulating variants. High efficacy indicates strong protection, but no vaccine guarantees 100% prevention. Overall, vaccines are an effective tool in reducing disease severity, transmission, and outbreaks.