Sisonke 2 - A COVID-19 Vaccine Boost Open Label Study.

Purpose To evaluate the effectiveness and safety of the single dose Ad26.COV2.S (Jansen) COVID-19 vaccine plus a homologous boost with Ad26.COV2.S (Janssen) COVID-19 vaccine among Sisonke participants as compared to unboosted Sisonke participants In addition the investigators will continue to evaluate VE of the Sisonke Boost compared to: i) Vaccinated populations pre boosts ii) Unvaccinated populations in South Africa. Study design Open-label, single-arm phase 3B vaccine implementation study Rationale South Africa is severely affected by the global COVID-19 epidemic, and following the initial prime vaccination among HCWs in the first 4 months of 2021. New data has demonstrated the safety and effectiveness of a booster dose given two months or more after the initial Ad26.COV2.S. This provides the rationale and feasibility for the evaluation of a homologous booster vaccine dose to the cohort of vaccinated Sisonke participants to inform the larger vaccine rollout. Study participants Sisonke participants age 18 and over working in the South African public and private health care sector (approx N=500 000) who were enrolled in Sisonke and have not subsequently had a further booster vaccine dose. Study sites Department of Health Vaccine Administration Sites across South Africa supported by the Sisonke (Together) (VAC31518COV3012) Trial Research Site Investigators and Study Staff Study duration Participants will receive a homologous Ad26.COV2.S (Janssen) booster dose of vaccine at least 6 months post the prime vaccination. The investigators will monitor outcomes utilising the DATCOV surveillance system and NHLS/NICD SARS COV-2 testing databases for up to 2 years post initial vaccination. Study products Ad26.COV2.S by Janssen administered as a single dose followed by a single booster injection. Primary objectives • To assess the effectiveness of Ad26.COV2.S vaccine as a homologous boost on severe COVID, hospitalizations and deaths in Sisonke participants as compared with the unboosted Sisonke populations. Secondary objectives To assess the effectiveness of Ad26.COV2.S vaccine as a homologous boost on severe COVID, hospitalizations and deaths in Sisonke participants as compared vaccinated and unvaccinated populations of essential workers in South Africa. * To estimate the incidence of symptomatic SARS CoV-2 infections in Sisonke participants following a boost compared with the unboosted Sisonke populations and general vaccinated and unvaccinated population in South Africa * To estimate booster dose uptake among Sisonke participants in South Africa * To monitor the genetic diversity of breakthrough SARS CoV-2 infections. * To monitor safety in the case of homologous boosts in Sisonke participants.