The AstraZeneca US Phase III trial of AZD 1222 (Covishield in India) demonstrated a statistically significant vaccine efficacy of 79% at preventing symptomatic COVID-19 and 100% efficacy at preventing severe disease and hospitalization. In this double-blinded, placebo-controlled multicenter trial, safety and efficacy were analyzed. The trial included 32,449 participants accruing 141 symptomatic cases of COVID-19. The trial had a 2:1 randomization of vaccine to placebo.
AstraZeneca’s vaccine was co-developed by the University of Oxford and its spin-out company, Vaccitech. It uses a replication-deficient chimpanzee viral vector based on a weakened version of a common cold virus (adenovirus) that causes infections in chimpanzees and contains the genetic material of the SARS-CoV-2 virus spike protein. After vaccination, the surface spike protein is produced, priming the immune system to attack the SARS-CoV-2 virus if it later infects the body. In the current trial, 20% of participants were 65 years and above and approximately 60% had co-morbidities that increase the risk of having severe COVID-19.
The participants received two doses administered at a four-week interval. Trials have shown that an extended interval of up to 12 weeks demonstrated greater efficacy, which was also supported by immunogenicity data. This evidence suggests administration of the second dose with an interval longer than four weeks could further increase efficacy. This would also increase the number of available doses enabling widespread vaccine coverage. There was no increased risk of thrombosis or events characterized by thrombosis. Trial results also revealed that there was comparable efficacy of the vaccine across ethnicity and age, with 80% efficacy in participants aged 65 years.
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