South Africa will roll out AstraZeneca's coronavirus vaccine in a "stepped manner" to assess its ability to prevent severe illness, Professor Salim Abdool Karim, co-chair of South Africa's Ministerial Advisory Committee on COVID-19, said on Monday.
South Africa said on Sunday it would put on hold its use of the AstraZeneca shot after research showing it was only minimally effective in preventing mild-to-moderate illness against a variant of the coronavirus now dominant in the country.
Speaking to a briefing of the World Health Organization (WHO), Abdool Karim said it was too early to say whether the AstraZeneca vaccine would still be effective in preventing serious disease, as there was not yet enough data on its effectiveness in older people against the variant.
South Africa would pause its rollout of the AstraZeneca vaccine for now while determining the next steps, and could vaccinate 100,000 people with the shot to see how well it worked on preventing hospitalisations and deaths.
"We don't want to vaccinate people with a product which may not prevent hospitalisation or reduce disease," Abdool Karim said.
He said South Africa would initially roll out Johnson & Johnson's vaccine instead, so the change in plans would not have a major impact on the pace of South Africa's vaccination programme.
The AstraZeneca vaccine accounts for nearly all doses - more than 330 million - that the WHO's COVAX programme intends to distribute to poor countries in a first phase, beginning as soon as this month.
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Seth Berkeley, chief executive of the GAVI alliance which co-leads the COVAX programme, said the issue was still being studied, but suggested there were no plans to reject the vaccine for now.
He noted that the South African study used a dosing schedule of four weeks between the first and second dose, and that evidence had since suggested that the AstraZeneca vaccine becomes more effective with a longer gap between doses.
Kate O'Brien, head of immunisations at the WHO, said information would continue to come in to refine plans to use vaccines, and it was "important to steer a steady ship."