Data from laboratory studies show Johnson & Johnson's Covid-19 vaccine works well against the Delta variant that now dominates new infections in South Africa, the head of the country's Medical Research Council said on Friday.

"All the data that we see indicate good immediate and sustained immune response against Delta, and we see surprising durability in the immune response for the single dose J&J right up to eight months," Glenda Gray told a news conference.

South Africa is using the J&J and Pfizer vaccines in its immunisation campaign.