1. World Health Organization Websitehttps://www.who.int/publications/m/item/weekly-epidemiological-update-on-covid-19---13-april-2021
2. Pfizer and BioNTech Achieve First Authorization in the World for a Vaccine to Combat COVID-19https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-biontech-achieve-first-authorization-world
3. Press Releasehttps://investors.modernatx.com/news-releases