BENGALURU/LONDON (Reuters) — The United States has secured almost a third of the first 1 billion doses planned for AstraZeneca’s experimental COVID-19 vaccine by pledging up to $1.2 billion, as world powers scramble for medicines to get their economies back to work.

While not yet proven to be effective against the coronavirus, vaccines are seen by world leaders as the only real way to restart their stalled economies, and even to get an edge over global competitors.