One safety signal identified in post-authorization surveillance studies of both vaccines is an association with rare blood clotting events with low platelet counts - thrombosis with thrombocytopenia syndrome (TTS) and vaccine-induced thrombotic thrombocytopenia (VITT) - which were not observed in the Phase 3 trials. In post-authorization studies, both the Oxford-AstraZeneca and J&J/Janssen COVID-19 vaccines have been demonstrated to be safe. However, like mRNA vaccines, their effectiveness varies against different SARS-CoV-2 variants ( see Emerging Variants ) and appears to wane over time ( see Immunity page ). Finally, the Gam-COVID-Vac vaccine (Sputnik V), developed by the Gamaleya Research Institute of Epidemiology and Microbiology in Russia, is another viral vector vaccine that uses two human adenovirus vectors, (Ad26 and Ad5), both of which encode for the SARS-CoV-2 spike protein.īoth the Johnson & Johnson/Janssen and Oxford-AstraZeneca COVID-19 vaccines are highly effective against both symptomatic and severe COVID-19 across age groups and in diverse populations (see literature subsections for Johnson & Johnson/Janssen and Oxford-AstraZeneca ). It encodes for the spike protein of SARS-CoV-2. This vaccine uses a chimpanzee adenovirus (ChAdOx1, which is based on ChAdY25) as the viral vector. The Oxford-AstraZeneca COVID-19 vaccine is another viral vector vaccine that has been authorized for use in many countries. This vaccine uses a human adenovirus, Ad26, as the viral vector, and encodes for a stabilized variant of the SARS-CoV-2 spike protein. under emergency use authorization by FDA. The Johnson & Johnson/Janssen COVID-19 is the only viral vector vaccine currently available in the U.S. Several COVID-19 vaccines are based on this technology, including the Johnson & Johnson/Janssen, Oxford-AstraZeneca and Gam-COVID-Vac (Sputnik V) vaccines. Nonreplicating viral vector vaccines infect cells, resulting in the production of the vaccine antigen, but the viral vector cannot be reproduced (van Riel, July 2020 ). The only currently licensed replication-competent vaccines are the recombinant vesicular stomatitis virus (rVSV)-Zaire Ebola virus vaccine and the live attenuated tetravalent dengue vaccine. The viral vector is also produced and is then able to infect new cells, which then create more viral antigen. Replicating viral vector vaccines infect cells, resulting in the production of the vaccine antigen. Viral vector vaccines can be replicating or nonreplicating: The antigen is then expressed on the host cell surface, resulting in the induction of an immune response. ![]() In the nucleus, the genes of the pathogen are expressed, resulting in the creation of the antigen. The vaccine delivers the vector, which infects host cells DNA virus vectors (like adenoviruses) then travel to the nucleus. The vector is a virus different from the one the vaccine is targeting (for example, an adenovirus). ![]() ![]() Genes of a pathogen - typically those that code for specific antigens that elicit a protective immune response - are first inserted into the genome of a viral vector. Viral vector vaccines utilize viruses to deliver genes that encode vaccine antigens into host cells ( Vrba, November 2020 ). Some sections may reflect more recent updates. This page undergoes regular review and was last comprehensively reviewed on Nov ember 1, 2022. Johnson & Johnson/Janssen COVID-19 Vaccine.
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