1. Single-dose of Ad26.COV2.S reduces risk of COVID-related hospitalization by 67% compared to matched unvaccinated control group.

2. Breakthrough infections in the vaccinated group were only severe in 0.5% of reported cases.

Evidence Rating Level: 2 (Good)

Study Rundown: The Sisonke study aimed to provide a vast amount of Ad26.COV2.S vaccines for healthcare workers in South Africa. The study successfully vaccinated 477 102 healthcare workers of which 215 813 were matched to unvaccinated controls in the general population and included for data analysis. This large sample size was monitored between time of vaccination (earliest date of Feb 17, 2021) and July 17, 2021. During this period, the beta (B.1.351) and Delta (B.1.617.2) were the dominant variants. Through an electronic healthcare database, any hospitalizations or deaths related to COVID-19 were recorded. Participations were also encouraged to contact the study team to report any adverse events or breakthrough infections. The study found that a single-dose of Ad26.COV2.S reduced risk of hospitalization from COVID-19 by 67% and death from COVID-19 by 83%. Limitations to this study include the inability to analyze the risk of overall infection with COVID-19 and took place before the emergence of the Omicron variant. Nonetheless, this study provides useful data on the effectiveness of a single-dose vaccine in areas where intensive vaccination programs may be difficult to roll-out.

Click to read the study in the Lancet

Relevant Reading: National COVID-19 Hospital Admissions and Mortality Among Healthcare Workers in South Africa, 2020-2021

In-Depth [prospective cohort study]: The Sisonke study is a single-arm, open-label, phase 3B trial of single-dose Ad26.COV2.S (Johnson & Johnson) in healthcare workers across all regions of South Africa. Eligibility criteria included patient-facing and non-patient-facing healthcare workers aged 18 years and older. Adverse events were monitored by passive surveillance with contact information provide where participants were encouraged to share adverse events or breakthrough infections. Data on breakthrough infection, hospitalizations and deaths were gathered via a pre-existing database for individuals admitted to hospital for COVID19 and the National Population Register. Enrollment occurred between Feb 17-Mar 17, 2021, and data collection was until July 17, 2021. Vaccinated participants were matched to members of the general population. A total of 215 813 participants received the vaccine with an equal amount of unvaccinated matched controls identified. 74.9% of the eligible healthcare workers were female and the average age of participants was 42.0 years. The vaccine was seen to reduce the risk of COVID-19-related hospitalizations by 67% and COVID-19-related deaths by 83%. Breakthrough infections did occur in the vaccinated group but were severe in only 0.5% of cases.

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