Vast majority of breakthrough infections in vaccinated health workers are mild

Cape Town | 1 July 2021 | Given the intensity of the third wave and spread of the delta variant, the Sisonke investigators would like to update health workers and the public regarding new data on the JnJ vaccine, and the pattern of breakthrough infections in our health workers vaccinated as part of the phase 3b study.

Breakthrough infections following the JnJ vaccine are defined as a positive COVID-19 test more than 28 days following vaccination. Some people test positive on routine screening (for example when being admitted to hospital for a non-COVID-19 procedure or following exposure at work) and some following development of symptoms or contact with another person with COVID-19. We track these through daily linkages to national COVID-19 registries of laboratory and hospitalisation data and through reports to the Sisonke desk. These are then passed onto our breakthrough infection team who confirm the infection and timing, make contact with the health worker and if appropriate attending doctor, and establish the severity of the infection. Consistently we are finding that 94% of breakthrough infections are mild, 4% are moderate and only 2% severe.

Report breakthrough infections: We encourage health workers who get COVID-19 or admit a vaccinated health worker to be in touch so that we can assess severity of infection, and if severe arrange for immediate sequencing of the virus from the affected health worker. We aim to sequence all severe infections. This week sequencing shows a similar pattern of variants to that in the general population with predominance of beta and delta variants. These findings are in line with other new data suggesting that a single-dose of the JnJ vaccine protects against variants of concern
including the delta variant. Health workers can report breakthrough infections by:

1. Entering their details onto our online self-reporting tool:
2. Emailing us at:
3. Calling the Sisonke desk at: 0800 014 956
Emails and the Sisonke desk are staffed Monday to Friday 8am to 5pm and Saturday 8am to 1pm.

New laboratory and immunogenicity (antibody) studies from the United States show that over time that immune responses induced by the JnJ vaccine mature and covers variants of concern such as the beta and delta variants. More details will be available within the next week following scientific publication. We are replicating laboratory virus neutralisation studies using serum from health workers who enrolled in our more detailed Sisonke sub-studies. Co-principal investigator Professor Glenda Gray notes that “the single dose vaccine, designed for emergency use is safe and easy to use. We have mounting data to suggest that immunity increases over time and that it retains its efficacy against important variants such as beta and delta.”

Co-principal investigator Professor LindaGail Bekker adds “keeping individuals out of ICU and off ventilators is an important outcome. I’m very reassured that the vast majority of breakthrough infections in Sisonke are mild. We believe that recommending booster top-ups with another vaccine is premature. We hold in mind that South Africa has only vaccinated 3 of the 41 million people it needs to safeguard its people against severe COVID-19”.

The Sisonke study is already demonstrating the valuable contribution of a partnership between science and government to undertake research in real-world circumstances to enrich our understanding of COVID-19 vaccines. It has established safety and breakthrough monitoring systems for use in the wider National Vaccination Programme and will continue to provide robust evidence to guide South Africa’s vaccine choice to ensure that every jab delivered into arms counts towards saving lives.

About the Sisonke Study:
The Sisonke study is a collaboration between the National Department of Health, South African Medical Research Council, Desmond Tutu Health Foundation, CAPRISA, Janssen and Johnson & Johnson. This open label, single-arm Phase 3b vaccine clinical trial of the investigational single-dose Janssen COVID-19 vaccine candidate aims to monitor the effectiveness of the investigational single-dose Janssen vaccine candidate at preventing severe COVID-19, hospitalizations and deaths among healthcare workers as compared to the general unvaccinated population in South
Africa. Health workers who received a Sisonke vaccine will be followed for a period of two years.

Dumile Mlambo
Public Relations Manager: SAMRC
Tel: +27 21 938 0407
Cell: +27 78 313 5798