GENEVA, Jan. 22 (Xinhua) -- COVAX, the global initiative led by the World Health Organization (WHO) to ensure rapid and equitable access to COVID-19 vaccines for all countries, said on Friday that it will purchase up to 40 million doses of the Pfizer-BioNTech vaccine. Rollout of the Pfizer-BioNTech vaccine, which has already received WHO emergency use listing, will commence with the successful negotiation and execution of supply agreements, according to a COVAX announcement. The global initiative also confirmed that it will exercise an option to receive its first 100 million doses of the AstraZeneca/Oxford University-developed vaccine manufactured by Serum Institute of India (SII), as per an existing agreement with the SII. The majority of the 100 million doses are earmarked for delivery in the first quarter of the year.