Pfizer has said its vaccine's efficacy drops over time, citing a study that showed 84% effectiveness from a peak of 96% four months after a second dose.
These therapies - artesunate, imatinib and infliximab - were selected by an independent expert panel for their potential in reducing the risk of death in hospitalised COVID-19 patients
At least 2.6% of the world's population has been infected
The countries reporting the most cases on a seven-day average - the United States, Brazil, Indonesia, India and Iran - represent about 38% of all global cases reported each day.
We cannot accept countries that have already used most of the global supply of vaccines using even more of it, says WHO director general Adhanom Ghebreyesus
First detected in India, the variant has been recorded in 15 out of the 22 countries of the region under its purview, stretching from Morocco to Pakistan
In a closed-door briefing to members states, WHO chief Tedros Adhanom Ghebreyesus said one priority in the probe should be "audits of relevant laboratories and research institutions operating in the area of the initial human cases identified in December 2019".
Striking an increasingly exasperated tone, the WHO said the world would look back on itself with shame if it knowingly chose to leave the world's weakest at the mercy of the pandemic.
"The Delta variant is ripping around the world at a scorching pace, driving a new spike in COVID-19 cases and death," Tedros said.
"It has to be based on the science and the data, not on individual companies declaring that their vaccines need to be administered as a booster dose," she said.
"The agreements, which come at a time when the Delta variant is posing a rising risk to health systems, will begin to make 110 million doses immediately available to participants of the COVAX Facility, with options for additional doses," GAVI said.