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•   OFFERS AN ADVANTAGE  As of mid-2021, the covid-19 vaccine ChAdOx1-S has been primarily evaluated in four comparative clinical trials, including about 24 000 adults, as well as in epidemiological studies. In the context of an epidemic of infection by coronavirus Sars-CoV-2, the covid-19 vaccine ChAdOx1-S reduces the short-term risk of symptomatic covid-19 and hospitalisation for covid-19, including in elderly subjects and when the so-called UK (or Alpha) variant of the virus is present. It may not be effective against the so-called South African (or Beta) variant. There are still unknowns concerning the duration of protection and the effect of the vaccine on transmission of the virus. The adverse effects in the short term are those shared by most vaccines, in particular frequent local and systemic reactions. During the course of the vaccination campaigns, flulike symptoms (sometimes severe) have been reported frequently, as well as an increased risk of certain rare but serious thrombotic events. There are still unknowns regarding the long-term adverse effect profile of this vaccine, given its limited history of use. In practice, given the serious nature of the thrombotic events associated with the covid-19 vaccine ChAdOx1-S, it should probably be regarded as a second-choice option, behind the mRNA vaccines already available. However, it is easier to deploy than the mRNA vaccines, especially in a community setting, even though the multi-dose format is not ideal. As of mid-2021, as with the other vaccines, it complements other preventive measures, but does not replace them. 

©Prescrire 1 September 2021

Source: "Viral vector covid-19 vaccine ChAdOx1-S (Vaxzevria°) and covid-19. Efficacy in the short term, but a risk of rare, sometimes fatal, thrombosis" Prescrire International 2021; 30 (229): 201-203. Subscribers only.

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