Preliminary results from the Phase 3b Sisonke study in South African healthcare workers show that a homologous booster shot of the Johnson & Johnson COVID-19 vaccine demonstrated 85% effectiveness against COVID-19-related hospitalisation during the 4th wave of the pandemic driven by the Omicron variant. The study that hasn’t been peer-reviewed, was conducted by the South African Medical Research Council (SAMRC).  During the period studied (mid-November to mid-December) the frequency of Omicron increased from 82 to 98% of COVID-19 cases in South Africa.

Sisonke 2 was conducted in approximately 350 vaccination centers across all nine provinces of the country from 15 November to 20 December with more than 69 000 healthcare workers receiving the booster shot in the period under investigation.

“Data from the Sisonke 2 study confirm that the Johnson & Johnson COVID-19 booster shot provides 85% effectiveness against hospitalisation in areas where Omicron is dominant. This adds to our growing body of evidence which shows that the effectiveness of the Johnson & Johnson COVID-19 vaccine remains strong and stable over time, including against circulating variants such as Omicron and Delta,” said the Global Head, Janssen Research & Development, LLC, Johnson & Johnson, Mathai Mammen in a statement.

 “We believe that the protection could be due to the robust T-cell responses induced by the Johnson & Johnson COVID-19 vaccine. Furthermore, these data suggest that Omicron is not affecting the T-cell responses generated by our vaccine,” Mammen added.

“Even before you factor in the increased infectiousness of Omicron, we have to remember that healthcare workers on the frontlines are at a greatly increased risk of being affected by COVID-19 in the first place,” said SAMRC President and CEO, Prof Glenda Gray.

“We are therefore encouraged to see that boosting with the Johnson & Johnson COVID-19 vaccine regimen provides strong protection in a challenging real-world setting where there is an elevated risk of exposure – not just to COVID-19, but to the highly transmissible Omicron variant.”

According to the Deputy Director General of the the Department of Health, Dr Nicholas Crisp, the data showing the effectiveness of the Ad26.COV.2 vaccine booster against Omicron in Sisonke are important, as this vaccine is part of the arsenal to combat COVID-19.

“This data should reassure healthcare workers who have not taken their booster to get vaccinated as soon as possible,” Dr Crisp said.

The data have been submitted to the pre-print server medRxiv by the studies’ authors, with anticipation of publication in peer-reviewed journals.