The Biden administration is buying 500 million doses of Pfizer’s coronavirus vaccine to donate to the world as the United States dramatically increases its efforts to help vaccinate more of the global population, three people familiar with the plans said Wednesday.

The first 200 million doses will be distributed this year, with the subsequent 300 million shared in the first half of next year. The doses will be distributed by Covax, the World Health Organization-backed initiative to share doses around the globe, and they will be targeted at low- and middle-income countries.