The U.S. has administered 200 million doses of COVID-19 vaccine, a White House official said Friday.

Just under 40 per cent of Americans have had at least one dose, and about a quarter have completed the one- and two-dose vaccinations. The news was announced on Twitter by Cyrus Shahpar, the White House COVID-19 Data Director.

The vaccine rollout has been accelerating as supply increases, with the U.S. giving shots to about 1 per cent of the population every day, according to the Bloomberg Vaccine Tracker. It took the U.S. 89 days to administer the first 100 million doses, a milestone reached on March 12. The second 100 million has come in just 36 days.

President Joe Biden has said his goal was to administer 200 million doses in the first 100 days of his administration. Because vaccination was started under Donald Trump’s administration, it will take another 16.5 million doses to reach Biden’s mark. That should happen some time next week, about a week ahead of Biden’s deadline.

That target will be slightly more difficult to reach because of a pause in the use of Johnson & Johnson’s vaccine as health regulators investigate reports of dangerous blood clots. It’s not clear when use of those shots will resume. A panel of expert advisers has indicated they’ll take at least another week to study the issue.

The pause in J&J’s vaccines won’t have a major impact in the short term -- the vast majority of doses that are being distributed in the U.S. are shots made by Pfizer Inc. and its German partner BioNTech SE, and by Moderna Inc. But the one-dose J&J vaccines are important to the U.S. supply in the longer term, and the fact that they are a single dose makes them easier to use, especially for harder to reach populations.

There are also signs that even as the government arranges for the distribution of tens of millions of doses a week, supply is beginning to build up in certain locations. A handful of states now have more than 30 per cent of the doses sent to them still unused, Bloomberg reported on Thursday.

Some of that growing surplus may represent an expected inefficiency as vaccines are sent to more locations and many of the most enthusiastic people have gotten shots. But there are also signs in some places, such as Lynchburg, Virginia, that vaccine appointments are going unfilled, even though a lower-than-average portion of the local population has been vaccinated.