In clinical trials of the Covid vaccine currently in use, effectiveness rates range from 50% to 95%. That rate means that in the experimental group of volunteers who received the vaccine, cases of Covid were between 50% and 95% lower than in the group of volunteers who received a placebo. On an individual basis, an effectiveness rate of, say, 80%, means that a vaccinated person’s risk of disease is about 20% compared with a similarly unvaccinated person. However, a vaccine’s real-world performance, known as its effectiveness, is not necessarily the same as its effectiveness in a study under controlled conditions. And both potency and potency can vary for the same vaccine across the populations, timing and regimen used; This rate is influenced by many factors, including the SARS-CoV-2 variants present and compliance with public and social health measures to prevent transmission of the virus.
https://www.washingtonpost.com/business/why-the-vaccinated-are-still-at-risk-from-coronavirus/2021/07/21/2fdf4b1e-ea96-11eb-a2ba-3be31d349258_story.html?utm_source=rss&utm_medium=referral&utm_campaign=wp_business | Why the Vaccinated Are Still at Risk From Coronavirus