A day after South Africa announced it was putting on hold the rollout of a Covid-19 vaccine that has raised questions about reliability, the head of the World Health Organization (WHO) said that the emergence of new coronavirus variants has raised major questions on whether available vaccines will be effective.

Speaking during WHO’s latest press briefing from Geneva on Monday, February 8, Dr Tedros Adhanom Ghebreyesus noted that the Oxford-AstraZeneca vaccine is one of several that has been shown to be effective in preventing severe disease, hospitalization and death from Covid-19.

But he acknowledged that the emergence of new variants of the virus "has raised questions" about the potential impact of those variants on vaccines.

Tedros said: "Yesterday (Sunday), South Africa announced it was putting a temporary hold on the rollout of the Oxford-AstraZeneca vaccine after a study showed it was minimally effective at preventing mild to moderate disease caused by a variant first identified in South Africa."

In the study, some 2,026 participants took part in the trial, according to Prof Salim Abdool Karim, co-chair of South Africa’s Ministerial Advisory Committee on Covid-19.  

"This is clearly concerning news. However, there are some important caveats," Tedros said, adding that given the limited sample size of the trial and the younger, healthier profile of the participants, "it is important to determine whether or not the vaccine remains effective in preventing more severe illness."

The WHO boss noted that these results are a reminder that "we need to do everything we can to reduce circulation of the virus with proven public health measures."

It is noted that while the overall efficacy of the AstraZeneca vaccine was 66 per cent in the larger study that includes the UK, Brazil and South Africa, the South African data on its own showed only 22 per cent efficacy.

"We know from the overall trial that the AstraZeneca vaccine is effective against other pre-existing variants. We’re just not confident about its efficacy against the 501Y.V2 variant," Karim said.

Karim said they are considering a proposal to rollout the vaccine among 100,000 people initially, and monitoring their hospitalization rates based on a threshold.  

The country also plans to move ahead with deploying vaccines made by Pfizer/BioNTech and Johnson and Johnson, according to media reports. 

Public's role in protecting vaccines 

Several countries are succeeding in suppressing transmission, Tedros said, including those where new variants are circulating.

"We all have a role to play in protecting vaccines," Tedros said.

"Every time you decide to stay at home, to avoid crowds, to wear a mask or to clean your hands, you are denying the virus the opportunity to spread, and the opportunity to change in ways that could make vaccines less effective."

He noted that 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.

"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."

The WHO has a mechanism for tracking and evaluating variants of the virus that causes Covid-19.

Tedros said they are now expanding that mechanism to provide guidance to manufacturers and countries on changes that may be needed for vaccines.

"These developments highlight why it’s so important to scale up manufacturing and roll out of vaccines as quickly as possible and as widely as possible to protect people before they are exposed to new variants."

WHO’s Strategic Advisory Group of Experts on Immunization, or SAGE, met on Monday to review the Oxford-AstraZeneca vaccine and to discuss the new developments. 

On Tuesday, February 9, Tedros said he will meet with the chair of SAGE to discuss its recommendations.

"In the next few days, WHO expects to make a decision on the emergency use listing of the Oxford-AstraZeneca vaccine, for the two sites in India and the Republic of Korea which will produce it for COVAX."