The United States reaped the fruits of its vaccination campaign against Covid-19 as it became the first nation to reach 100 million people, but Europe's rollout faced fresh impediments and South America tightened restrictions in the face of Brazil's soaring infections, AFP reported.

The United States reported surging job growth and loosened travel curbs as it reached around half of its adult population with at least one dose, with President Joe Biden vowing to cover the vast majority within weeks.

But infections remain on the rise in parts of the United States, prompting Biden to urge Americans to keep wearing masks and taking other precautions to stop the pandemic that has killed more than 2.8 million people worldwide.

The United States has suffered a catastrophic Covid toll at more than 550,000 people dead, with health measures polarising the country since last year when Biden's predecessor Donald Trump criticized restrictions.