The World Health Organization (WHO) has warned against jumping to conclusions about the efficacy of coronavirus vaccines.

This is after a South African study suggested that the AstraZeneca jab was less effective against a local variant of the virus.

But experts are hopeful that the vaccine will still be effective at preventing severe cases.

Head of WHO, Tedros Adhanom Ghebreyesus, said data used in the study was from a "limited sample size" and the participants were "younger and healthier".

"It is important to determine whether or not the vaccine remains effective in preventing more severe illness," he said in a statement.

But he acknowledged that manufacturers of vaccines will have to adopt to mutations of the coronavirus.

"It seems increasingly clear that manufacturers will have to adjust to the evolution of the virus, taking into account the latest variants for future shots, including boosters.

"We know viruses mutate and we know we have to be ready to adapt vaccines so they remain effective," he said.