A COVID‑19 vaccine is a vaccine intended to provide acquired immunity against severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2), the virus causing coronavirus disease 2019 (COVID‑19). Prior to the COVID‑19 pandemic, work to develop a vaccine against coronavirus diseases like severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) established knowledge about the structure and function of coronaviruses; this knowledge enabled accelerated development of various vaccine technologies during early 2020.[1]
As of February 2021, 66 vaccine candidates are in clinical research, including 17 in Phase I trials, 23 in Phase I–II trials, 6 in Phase II trials, and 20 in Phase III trials.[2] Trials for four other candidates were terminated.[2] In Phase III trials, several COVID‑19 vaccines demonstrate efficacy as high as 95% in preventing symptomatic COVID‑19 infections. As of February 2021, ten vaccines are authorized by at least one national regulatory authority for public use: two RNA vaccines (the Pfizer–BioNTech vaccine and the Moderna vaccine), three conventional inactivated vaccines (BBIBP-CorV, Covaxin, and CoronaVac), four viral vector vaccines (Sputnik V, the Oxford–AstraZeneca vaccine, Convidicea, and the Johnson & Johnson vaccine), and one peptide vaccine (EpiVacCorona).[2]
Many countries have implemented phased distribution plans that prioritize those at highest risk of complications, such as the elderly, and those at high risk of exposure and transmission, such as healthcare workers.[3] As of 17 February 2021, 188.35 million doses of COVID‑19 vaccine have been administered worldwide based on official reports from national health agencies.[4] Pfizer, Moderna, and AstraZeneca predicted a manufacturing capacity of 5.3 billion doses in 2021, which could be used to vaccinate about 3 billion people (as the vaccines require two doses for a protective effect against COVID‑19). By December 2020, more than 10 billion vaccine doses had been preordered by countries,[5] with about half of the doses purchased by high-income countries comprising 14% of the world’s population.[6]
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