The World Health Organization gave emergency use approval to AstraZeneca's COVID-19 vaccines on Monday, meaning distribution can start to poorer countries starved of doses to fight the pandemic.
The AstraZeneca-Oxford jab forms the bulk of batches being lined up through Covax, the global program aimed at procuring and shipping out vaccines equitably around the world, regardless of wealth.
It is only the second COVID-19 jab to have received WHO authorization, after the Pfizer-BioNTech vaccine.
"The WHO today listed two versions of the AstraZeneca-Oxford COVID-19 vaccine for emergency use, giving the green light for these vaccines to be rolled out globally through Covax," the UN health agency said in a statement.
The two versions given the seal of approval are being produced by the Serum Institute of India (SII), and by SKBio in South Korea.
Separate reviews were needed for each production process, although the vaccine is the same.
"Countries with no access to vaccines to date will finally be able to start vaccinating their health workers and populations at risk, contributing to the Covax facility's goal of equitable vaccine distribution," said WHO assistant director general Mariangela Simao.
"But we must keep up the pressure to meet the needs of priority populations everywhere and facilitate global access. To do that, we need two things -- a scale-up of manufacturing capacity, and developers' early submission of their vaccines for WHO review."
337.2 million doses
The organization's emergency use listing procedure assesses the quality, safety, and efficacy of COVID-19 vaccines, and is a prerequisite for vaccines in the WHO co-led Covax facility.
AstraZeneca vaccines from India and South Korea made up almost all of the initial 337.2 million doses lined up for Covax's first wave of distribution, which is set to get moving in late February.
Some 145 participating economies are set to receive enough doses to immunize 3.3% of their collective population by mid-2021.
The first wave includes 240 million SII AstraZeneca doses; 96 million South Korean AstraZeneca doses; and 1.2 million Pfizer doses.
Both vaccines require two injected doses.
"We now have all the pieces in place for the rapid distribution of vaccines," WHO director-general Tedros Adhanom Ghebreyesus told a press conference.
Simao added: "There's no need to panic and no need for countries to go buying in the market, because they're going to pay more."
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OK for over-65s
Last week in a separate process, the WHO's Strategic Advisory Group of Experts on Immunization issued its interim usage recommendations for the AstraZeneca vaccine.
Soothing fears about the jab, SAGE concluded it could be used for people aged over 65, and also where coronavirus variants of concern are circulating.
SAGE acknowledged the lack of data on the vaccine's efficacy for over-65s, which has prompted a number of countries to withhold it from by far the most vulnerable age group.
But the experts decided that given its performance with younger adults, "it is likely that the vaccine will be found to be efficacious in older persons. The trial data indicate that the vaccine is safe for this age group."
They said the vaccine proved more effective when the interval between doses was extended to between eight and 12 weeks.
The number of reported COVID-19 cases globally has dropped for a fifth consecutive week, nearly halving from more than five million in the week of Jan. 4, to 2.6 million in the week starting Feb. 8.
"The fire is not out, but we have reduced its size. If we stop fighting it on any front, it will come roaring back," Tedros warned