https://www.scientificamerican.com/article/the-covid-cold-chain-how-a-vaccine-will-get-to-you/ > Two drug companies have now reported highly successful results from phase III trials of COVID-19 vaccines. On November 18 Pfizer and partner BioNTech said their vaccine was 95 percent effective at preventing the disease, based on full trial results. Two days earlier Moderna reported its vaccine was 94.5 percent effective, based on interim data. > Both Pfizer and Moderna use the same genetically engineered vaccine approach, which involves messenger RNA molecules. Assuming the U.S. Food and Drug Administration authorizes the vaccines for “emergency use,” each firm will have to ramp up production and distribution tremendously. Pfizer expects to produce up to 50 million doses worldwide in 2020 and up to 1.3 billion in 2021. Moderna intends to manufacture approximately 20 million doses in 2020 and 500 million to one billion in 2021. A person receiving either vaccine will need two doses, administered three or four weeks apart.