The U.S. economy grew at a robust 6.6% annual rate last quarter, slightly faster than previously estimated, the government said Thursday in a report that pointed to a sustained consumer-led rebound from the pandemic recession. But worries are growing that the delta variant of the coronavirus is beginning to cause a slowdown.

The report from the Commerce Department estimated that the nation’s gross domestic product — its total output of goods and services — accelerated slightly in the April-June quarter from the 6.5% it had initially reported last month. The economy’s expansion last quarter followed a solid 6.3% annual growth rate in the January-March period.

In recent weeks, many economists have been downgrading their estimates of GDP growth for this quarter, and for 2021 as a whole, as the now-dominant delta variant has sent confirmed COVID-19 cases rising throughout the country.