Many countries implemented phased distribution plans that prioritized those at highest risk of complications, such as the elderly, and those at high risk of exposure and transmission, such as healthcare workers. According to a June 2022 study, COVID‑19 vaccines prevented an additional 14.4 to 19.8 million deaths in 185 countries and territories from 8 December 2020 to 8 December 2021. The COVID‑19 vaccines are widely credited for their role in reducing the spread of COVID‑19 and reducing the severity and death caused by COVID‑19. However, immunity from the vaccines has been found to wane over time, requiring people to get booster doses of the vaccine to maintain protection against COVID‑19. Initially, most COVID‑19 vaccines were two-dose vaccines, with the sole exception being the single-dose Janssen COVID-19 vaccine. In 2020, the first COVID‑19 vaccines were developed and made available to the public through emergency authorizations and conditional approvals.

In January 2020, the SARS-CoV-2 genetic sequence data was shared through GISAID, and by March 2020, the global pharmaceutical industry announced a major commitment to address COVID‑19. The initial focus of SARS-CoV-2 vaccines was on preventing symptomatic, often severe illness. This knowledge accelerated the development of various vaccine platforms during early 2020. Prior to the COVID‑19 pandemic, an established body of knowledge existed about the structure and function of coronaviruses causing diseases like severe acute respiratory syndrome ( SARS) and Middle East respiratory syndrome ( MERS). A COVID‑19 vaccine is a vaccine intended to provide acquired immunity against severe acute respiratory syndrome coronavirus 2 ( SARS-CoV-2), the virus that causes coronavirus disease 2019 ( COVID‑19).

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