Meantime the Philippines and Thailand secured millions of doses, giving the shot a vote of confidence after experts raised questions about trial data earlier this week.
The UK government, which has secured 100 million doses of the vaccine, has targeted a rollout to begin before Christmas.
AstraZeneca's candidate is viewed as offering one of the best hopes for many developing countries because of its cheaper price and ability to be transported at normal fridge temperatures.
The Thai government signed a deal on Friday to procure 26 million doses of the vaccine and officials in the Philippines said they would secure 2.6 million shots and were negotiating a possible purchase of a further 1 million doses.
The announcements came after some scientists raised doubts about the robustness of results showing the shot was 90% effective in a sub-group of trial participants who, by error initially, received a half dose followed by a full dose.
AstraZeneca CEO Pascal Soriot said on Thursday that the drugmaker was likely to run an additional global trial to assess the efficacy of its vaccine using the lower dosage.
The company had released trial data on Monday that showed its experimental vaccine prevented on average 70% of COVID-19 cases in late-stage trials in Britain and Brazil.
While the success rate was 90% in the sub-group, some experts said the relatively small number of participants made it harder to be confident in the findings.
AstraZeneca said the administering of the half dose had been reviewed and approved by independent data safety monitors and the UK regulator, adding the regulator publicly confirmed that there was "no concern".
