A volunteer is administered the coronavirus vaccine developed by AstraZeneca and Oxford University, in Oxford, England. (Photo: AP)

The World Health Organization (WHO) Director-General Tedros Adhanom on Monday called for the adjustment of COVID-19 vaccines to factor in the new strains of the virus.

Tedros made the remarks at a media briefing on the COVID-19 pandemic, during which he noted South Africa's decision to halt its rollout of the Oxford-AstraZeneca vaccine after a study showed its jabs were minimally effective at preventing mild to moderate disease caused by a variant first identified the country.

"It also 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," said the WHO chief.

"We know viruses mutate and we know we have to be ready to adapt vaccines so they remain effective. This is what happens with flu vaccines, which are updated twice a year to match the dominant strains."

Tedros urged countries to continue reporting the emerging variants of the coronavirus to WHO in order to help coordinate global efforts to monitor their impact and advise countries accordingly.

He also called for the scaling up of manufacture and roll out of vaccines to protect people before they are exposed to new variants.