Different companies took different scientific approaches to developing the COVID-19 vaccine, which is good because taking multiple approaches increased the chance that at least one candidate would end up working. There are no guarantees for success at the beginning of a vaccine development process, so relying on just one would have been risky.
To date, career public servant-scientists at the US Food and Drug Administration (FDA) have granted Emergency Use Authorizations (EUAs) for both the Pfizer-BioNTech and Moderna COVID-19 vaccines. Before the EUAs were granted, independent experts serving on the FDA's vaccine advisory committee had voted overwhelming that, for people 16 years old and above (Pfizer-BioNTech), or 18 years old and above (Moderna), the benefits of the vaccines outweigh the risks. Canada and Britain have also cleared the Pfizer-BioNTech COVID-19 vaccine for use. There are limited doses of the vaccines, and it is expected the vaccines will first be made available to those considered most at risk to COVID-19 - health care workers and residents of long-term care facilities - although this will differ by state. For more information on the Pfizer-BioNTech COVID-19 vaccine, check out this nice FAQ from NPR. To read the FDA's fact sheet on the Moderna COVID-19 vaccine, click here.
There will be some differences in the vaccines that are ultimately expected to become available, such as how many doses you might need, how many days the doses are spaced apart, and the way the vaccine prompts your body to protect you against the virus.
Updated 19 December 2020