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Oxford Covid-19 Vaccine Trial

Trial sites

Officially called the Ox1CoV-19 vaccine VIDA-trial, the ‘Oxford trial’ was announced on 23 June 2020. Researchers began vaccinating human volunteers with a new vaccine called ChAdOx1 nCoV-19 on 24 June 2020.

The trial has enrolled volunteers at five sites in Gauteng and two in the Western Cape.

  • In Gauteng, the sites are in Hillbrow, Soweto, and Tshwane.
  • In the Western Cape, the sites are in Cape Town and Stellenbosch.


The study aims to enrol 1970 adult volunteers aged 18-65 years and who are HIV negative.

These participants should not have tested positive for Covid-19 and should not be pregnant or breast-feeding, nor have previously participated in a trial with an adenoviral vaccine or have received any other coronavirus vaccine.

The trial will also enrol 50 people living with HIV to examine the safety of the vaccine in this cohort and how well they respond to the vaccine.

Participants will need to provide written informed consent to participate in the trial and they will remain on the trial for approximately one year.

Trial implementation

Half of the participants will receive the ChAdOx1 COVID-19 vaccine and the other half (the control group) will receive a placebo (saline).

This random grouping of participants to receive either the vaccine or the placebo helps researchers understand participants’ response to ChAdOx1-Cov19, its safety, and whether the vaccine protects against Covid-19.

This is a double-blind study meaning neither participants nor investigators will not know until the end of the trial whether the participants received the CHADOX1-Cov19 vaccine or the control.

The objective of the trial is to investigate if the ChAdOx1-Cov19 vaccine will protect against Covid-19 without causing unacceptable side effects, and if it induces satisfactory immune responses.

The dose used in this trial was chosen based on previous experiences with other ChAdOx1-based vaccines and the study currently underway in the UK.

Participants will be given an E-diary to record any symptoms experienced for seven days after receiving the vaccine. They will also record if they feel unwell for the following three weeks.

Following vaccination, participants will attend a series of follow-up visits. During these visits, researchers will check participants’ observations, review the completed diaries, and take blood samples, which will be used to assess the immune response to the vaccine.

If participants develop Covid-19 symptoms during the study, they can contact a member of the clinical team who will assess them for infection. Should a participant become particularly unwell, they will be assisted to seek hospital care.


To assess whether the vaccine works to protect from Covid-19, statisticians in the research team will compare the number of infections in the placebo group with the number of infections in the vaccinated group. For this purpose, it is necessary for a small number of participants to contract Covid-19.

How quickly researchers reach the numbers required will depend on the levels of virus transmission in the community. If transmission remains high, enough data may become available in a couple of months to see if the vaccine works. If transmission levels drop, however, this could take up to six months or longer.


Although there are more than 100 COVID-19 vaccines currently in development, a significant proportion of vaccines that are tested in clinical trial are found not to be suitable for further development. The ChAdOx1-Cov19 vaccine is one of only five vaccines that are currently in the clinical development phase in humans, with the studies mainly being done in China, USA, UK, Australia and Europe. 

If this trial in South Africa is unable to show that the vaccine protects against COVID-19, or that it is not safe, progress will be reviewed and alternative approaches explored. The study is monitored intensely by an independent Data, Safety and Management Committee, which includes a leading South African scientist.

The protocol document is available for viewing here. A protocol is a document describing the background, rationale and objectives as well as the design, methodology, statistical considerations and organisation of a clinical research study.


Screening for Oxford COVID-19 vaccine trial participation is now closed.