Healthcare workers have until 14 January to get their Johnson & Johnson COVID-19 vaccine booster shots.
Phase 2 of the Sisonke vaccination programme kicked off in November, 10 months after the initial phase.
Researchers said that although the J&J jab did not prevent all Omicron coronavirus infections, it still prevented severe illness and hospitalisation.
Sisonke study co-lead investigator Professor Linda-Gail Bekker said that the booster shot does provide added protection even against the Omicron variant of concern.
Healthcare workers still wanting to get the jab after the 14 January cut-off date will have to join the queue as part of the national booster shot rollout.