The cohort was made of 45 healthy adults aged 18-55 who received two doses of 10 micrograms, 30 micrograms, or 100 micrograms of the mRNA jab, or a placebo.
The strongest immune response was in the 30 micrograms dose, while there was no notable difference in efficacy between that and the 100 micrograms, though the latter caused more side effects.
Last month, the US giant said the candidate was on track to start a planned Phase 2b/3 safety and efficacy trial, with regulatory review sought as early as October.
The pair are targeting global manufacturing of the first 100mln doses by the end of 2020 and another 1.3bn doses in 2021.
Americans will be immunised for free consistent with US government’s commitment for free access for COVID-19 vaccines.
The UK previously ordered 30mln doses.