Drugmaker Johnson & Johnson says it will be able to provide 20 million U.S. doses of its single-shot COVID-19 vaccine by the end of March, assuming it gets the greenlight from federal regulators.

J&J disclosed the figure ahead of a Congressional hearing on Tuesday looking at the country’s vaccine supply. White House officials cautioned last week that initial supplies of J&J’s vaccine would be limited.

The company reiterated that it will have capacity to provide 100 million vaccine doses to the U.S. by the end of June. That supply will help government officials reach the goal of having enough injections to vaccinate most adult Americans later this year. On a global scale, the company aims to produce 1 billion doses this year.

U.S. health regulators are still reviewing the safety and effectiveness of the shot and a decision to allow its emergency use is expected later this week. J&J’s vaccine would be the first in the U.S. that requires only a single shot.

Pfizer and Moderna vaccines require two doses spaced weeks apart. Executives from both companies and two other vaccine makers will also testify at Tuesday’s hearing.