Inactivated whole-virion SARS-CoV-2 vaccine reduces rates of symptomatic COVID-19 infections

1. Incidence of PCR-confirmed symptomatic COVID-19 cases was lower in the vaccine group compared with the placebo group (p<0.0001).

2. The majority of adverse events were mild and there was no vaccine-related mortality. 

Evidence Rating Level: 1 (Excellent)

Study Rundown: Inactivated vaccines offer a variety of benefits against transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). One such inactivated whole-virion vaccine is CoronaVac, which is currently in phase 3 trials in Brazil, Indonesia, Chile, and Turkey. This phase III randomized controlled trial aimed to assess the safety and efficacy of CoronaVac in Turkey. Primary outcome for this study was the proportion of laboratory confirmed COVID-19 cases at least 14 days after administering the second dose, while key secondary outcomes included incidence of hospitalization, adverse events, and mortality. According to study results, the vaccine group reported significantly fewer cases of symptomatic COVID-19 compared with placebo; however, the frequency of adverse events was higher in the former. In addition, no individuals in the vaccine group required hospitalization for their infection. While this study was well done, a major limitation was that it did not explore the impact of vaccine interchangeability on the aforementioned clinical outcomes. Nevertheless, it provides valuable insight into the use of CoronaVac for safe and effective immunogenicity during the COVID-19 pandemic.

Click to read the study in The Lancet

Relevant Reading: Effectiveness of an Inactivated SARS-CoV-2 Vaccine in Chile

In-depth [randomized controlled trial]: Between Sept 14, 2020, and Jan 5, 2021, 11 303 patients were assessed for eligibility across 24 centers in Turkey. Included patients were between 18-59 years of age with no previous history of COVID-19 and a negative SARS-CoV-2 PCR or antibody test. Those diagnosed with a bleeding disorder or on immunosuppressants were excluded. Altogether, 10 214 patients in the intention-to-treat group (65.1% in vaccine group vs. 34.9% in placebo group) and 10 029 patients in the per-protocol group (65.4% in vaccine group vs. 34.6% in placebo group) completed the trial. Median age among enrolled patients was 45 years (interquartile range [IQR] 37-51) and the majority (57.8%) were male.

The primary outcome of PCR-confirmed COVID-19 cases two weeks after receiving the second dose was lower in the vaccine group (31.7 cases per 1000 person-years, IQR 14.6-59.3) compared with the placebo group (192.3 cases per 1000 person-years, IQR 135.7-261.1; p<0.0001). This was also true with regard to the number of hospitalizations. More patients in the placebo group (36.4 hospitalizations per 1000 person-years, IQR 13.5-77.5) were admitted due to COVID-19 than in the vaccine group (0 hospitalizations per 1000 person-years), giving a 100% vaccine efficacy (95% confidence interval [CI] 20.4-100.0, p=0.0344). However, the incidence of serious adverse events was greater among patients in the vaccine group (n=1259, 18.9%) than in the placebo group (n=603, 16.9%, p=0.0108), with the most common systemic adverse event being fatigue (8.2% in vaccine group vs. 7.0% in placebo group, p=0.0228). There were no serious adverse events or mortality. Findings from this study suggest a high safety and efficacy profile for CoronaVac against symptomatic SARS-CoV-2 infection. 

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