Africa could have a Covid-19 vaccine in the first quarter of 2021 if human trials under way in South Africa succeed, a university professor heading the trials said on Thursday.

The ChAdOx1 nCoV-19 experimental vaccine is one of 19 being tested on humans globally in a race to find vaccines to stop a pandemic that has killed more than half a million people so far.

It is also being tested in Brazil by Oxford University scientists who are working with British drugmaker AstraZeneca on development and production.

“A vaccine could be made commercial as early as the beginning of next year,” said Shabir Madhi, professor of vaccinology at the University of Witwatersrand, who is leading the South African trial.

“But it is completely dependent on the results of clinical trials,” he cautioned, adding that out of the 19 potential vaccines being tried out, the most positive outcome would be if even two succeed.

Trials will depend on 2,000 volunteers aged 18-65 years who will be monitored for 12 months after vaccination to asses its efficacy.

Madhi, however, said early results could be seen by November or December.

“The timing of an efficacy read-out depends on when we have approximately 42 Covid-19 cases at least one month after vaccination,” he said.

Covid-19 cases in Africa topped half a million as of Wednesday, with almost 12,000 deaths.

Madhi said governments must put in an upfront purchase order for the potential vaccine.

A number of countries, including the United States and several in the European Union, have struck deals with drugmakers to reserve supplies of the experimental vaccines, even before they have been approved.

“[The] big challenge is we are looking at requiring billions of doses of vaccine. It is really going to be how companies can scale up and make it affordable and accessible,” said Pontiano Kaleebu, director at Uganda Virus Research Institute.

African manufacturers have not manufactured a single vaccine in the last 25 years, Madhi said.