1. Seroconversion at 84 days was greater in the ZyCoV-D group compared to placebo.
2. The occurrence of adverse events was comparable with one (not treatment-related) death occurring in each group.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Vaccines are crucial in the fight against COVID-19. Until now, vaccines have been manufactured by various healthcare agencies around the world. Many of these are RNA-based vaccines which must be stored at specific temperatures for viability. ZyCoV-D is a DNA-based vaccine produced by Cadila Healthcare that has been shown to be stable at storage temperatures of 2-8oC. However, little is known about its clinical effectiveness at the population level. This double-blind randomized trial aimed to evaluate the safety and efficacy of ZyCoV-D in patients with no SARS-CoV-2 infection at baseline. The primary outcome was prevalence of symptomatic RT-PCR-confirmed COVID-19 at day 84 (28 days after the third dose), while key secondary outcomes were frequency of severe COVID-19 cases and confirmed COVID-19 deaths. According to study results, patients assigned to the ZyCOV-D (vaccine) group developed a greater immunity response to SARS-CoV-2 compared to those in the placebo group. There were no reported cases of moderate or severe COVID-19 infection in the vaccine group. Conversely, the placebo group reported one severe and three moderate COVID-19 cases during the study period. A major limitation of this study may be the low number of total COVID-19 cases, with only 81 cases included in the efficacy analysis between both groups.
In-depth [randomized-controlled trial]: Between Jan 16 and June 23, 2021, 33 194 patients were screened for eligibility across 49 centers in India. Included were those aged ≥ 12 years with no known SARS-CoV-2 at baseline. Altogether, 27 701 patients (13 849 to ZyCoV-D and 13 852 to placebo) were included in the safety analysis. In the efficacy analysis, only 81 patients were eligible (20 to ZyCoV-D and 61 to placebo). The majority (67.1%) were male with a mean age of 36.5 years (standard deviation [SD] 13.8). Seroconversion at 84 days (i.e., 28 days after the third vaccine dose) was significantly greater in the ZyCoV-D group (n=44, 88.0%) compared to the placebo group (n=20, 42.6%; p<0.0001). The intervention group also reported greater antibody titres (26.7, 95% CI 17.4-41.0) compared to placebo (5.7, 95% CI 3.1-10.5). Moreover, the incidence of adverse events was comparable between both groups (n=623, 4.5% in the ZyCoV-D group vs. n=620, 4.5% in the placebo group), while overall vaccine efficacy was estimated to be 66.7%. Overall, findings from this study suggest that ZyCoV-D was both safe and effective in asymptomatic patients with no SARS-CoV-2 infection at baseline.
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