COVID-19 vaccine
A vaccine that trains the immune system to recognize SARS-CoV-2 and reduce the risk of COVID-19, especially severe disease.
mRNA vaccine: A vaccine that delivers messenger RNA encoding an antigen so cells produce that antigen and prompt an immune response. Some COVID-19 vaccines use mRNA to instruct cells to make the SARS-CoV-2 spike protein.
COVID-19 vaccine effectiveness: The degree to which COVID-19 vaccination reduces outcomes such as infection, symptomatic disease, hospitalization, or death. Effectiveness varies by outcome, time since vaccination, vaccine formulation, and circulating variant.
Operation Warp Speed: A U.S. government program launched in 2020 to accelerate development, manufacture, and distribution of COVID-19 vaccines and treatments. It funded and coordinated vaccine candidates before their efficacy was known.
Inactivated vaccine: A vaccine made from pathogens that have been killed so they cannot replicate. Some COVID-19 vaccines use inactivated whole virus rather than genetic instructions or purified protein.
Viral vector vaccine: A vaccine that uses a modified virus to deliver genetic instructions for an antigen into cells. Several COVID-19 vaccines use adenovirus vectors to deliver instructions for the spike protein.
Booster dose: An additional vaccine dose given after an initial series to strengthen or restore immune protection. Booster doses can raise waning protection, particularly against severe COVID-19.
COVID-19 vaccine clinical trials: Human studies evaluating the safety, immune response, and effectiveness of vaccines against COVID-19. Large randomized trials established evidence used in initial authorizations.
Live attenuated vaccine: A vaccine containing a weakened pathogen that can replicate but typically does not cause disease in healthy recipients. COVID-19 vaccines in common use generally avoid delivering a replicating SARS-CoV-2 virus.
Protein subunit vaccine: A vaccine containing selected pathogen proteins, often combined with an adjuvant to strengthen the immune response. This platform presents SARS-CoV-2 proteins directly rather than encoding them in cells.
Bivalent COVID-19 vaccine: A COVID-19 vaccine formulation designed to target two antigenic versions of SARS-CoV-2. Updated formulations have combined ancestral and variant spike targets.