Vaccine effectiveness against hospital admission in South African health care workers who received a homologous booster of Ad26.COV2 during an Omicron COVID19 wave: Preliminary Results of the Sisonke 2 Study. (preprint)

Following the results of the ENSEMBLE 2 study, which demonstrated improved vaccine efficacy of a two-dose regimen of Ad26.COV.2 vaccine given 2 months apart, we expanded the Sisonke study which had provided single dose Ad26.COV.2 vaccine to almost 500 000 health care workers (HCW) in South Africa to include a booster dose of the Ad26.COV.2. Sisonke 2 enrolled 227 310 HCW from the 8 November to the 17 December 2021. Enrolment commenced before the onset of the Omicron driven fourth wave in South Africa affording us an opportunity to evaluate early VE in preventing hospital admissions of a homologous boost of the Ad26.COV.2 vaccine given 6-9 months after the initial vaccination in HCW. We estimated vaccine effectiveness (VE) of the Ad26.COV2.S vaccine booster in 69 092 HCW as compared to unvaccinated individuals enrolled in the same managed care organization using a test negative design. We compared VE against COVID19 admission for omicron during the period 15 November to 20 December 2021. After adjusting for confounders, we observed that VE for hospitalisation increased over time since booster dose, from 63% (95%CI 31-81%); to 84% (95% CI 67-92%) and then 85% (95% CI: 54-95%), 0-13 days, 14-27 days, and 1-2 months post-boost. We provide the first evidence of the effectiveness of a homologous Ad26.COV.2 vaccine boost given 6-9 months after the initial single vaccination series during a period of omicron variant circulation. This data is important given the increased reliance on the Ad26.COV.2 vaccine in Africa.

The Impact of Routine Pulse Oximetry Use on Outcomes in COVID-19-Infected Patients at Increased Risk of Severe Disease: A Retrospective Cohort Analysis (preprint)

Background: A phenomenon of silent hypoxaemia has been described in patients with COVID-19 pneumonia, which is characterised by low oxygen saturation levels of < 90% in patients who appear clinically well and do not show signs of significant respiratory distress. We assessed the impact on clinical outcomes for high-risk COVID-19 patients using a pulse oximeter to monitor oxygen saturation levels in a home setting.Methods: We performed a retrospective cohort analysis using data from a large South African insurance administrator. Patients were categorised as high risk, based on age or if they had specific underlying clinical conditions, or if they were classified as high risk from predictive models based on medical scheme administrative claims data. The impact of pulse oximetry home monitoring on COVID-19 clinical outcomes were investigated by use of Cox proportional hazard models.Findings: Between 2 March 2020 and 31 October 2020, of 38 645 patients analysed, 8 113 were in the intervention group. The 60-day mortality rate for the evaluated high-risk population was 1·35%. After adjusting for the age and co-morbidity differences, the intervention group was found to have an adjusted hazard ratio (HR) of 0·52 (p<0·0001). No statistical significance was found between the intervened and control groups for admission to hospital, admission to ICU and, use of mechanical ventilation. The intervention group had a lower median CRP on admission (p=0·03), and after adjustment for admission CRP levels, elevated CRP was associated with increased mortality (p<0·0001), and the statistical significance in mortality between the intervention and the control group was lost.Interpretation: High-risk COVID19 patients who used a pulse oximeter to monitor oxygen saturation levels had significantly lower mortality rates, compared to other high-risk patients. The mortality benefit was explained by earlier presentation to hospital, as suggested by lower initial CRP levels.Funding Statement: None.Declaration of Interests: None.Ethics Approval Statement: Ethics clearance was obtained from the Human Research Ethics Committee (Medical) of the University of the Witwatersrand.