The study involved 499 medical workers - 100 receiving mixed doses, 200 taking two doses of the Pfizer/BioNTech shot and the remainder getting two AstraZeneca shots
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 doses are from an initial batch of 80 million US-made vaccines the Biden administration pledged last month to share globally amid concern about the disparity in vaccination rates between advanced and developing countries.
Johnson & Johnson's vector vaccine will contribute 18.3 million doses, and a total 70 million doses of vaccines from Sanofi, Novavax and Valneva will contribute the rest.