evidence: The COVID-19 vaccines coming soon to the United States and already approved in the U.K. and Canada are the fastest vaccines ever created. [...] The COVID-19 vaccines from Pfizer, Moderna and AstraZeneca make use of two of these new strategies, or "platforms," which makes them unlike any other commonly used vaccines. Most familiar vaccines — against flu, measles or tetanus, for example — rely on inactivated viruses (flu and tetanus) or weakened virus strains (measles, mumps), says Dr. Yang. Some vaccines, such as the one for hepatitis B, employ artificial proteins created in a lab. Each of these strategies requires development specific to the exact virus or bacterium. [...] The Pfizer and Moderna vaccines are based on the messenger RNA, or mRNA, platform. Hungarian biochemist Katalin Karikó — now a senior executive with BioNTech, Pfizer’s partner on the COVID-19 vaccine — started developing mRNA therapies in 1990 while a professor at University of Pennsylvania Medical School.