The Australian dollar - seen as a liquid proxy for risk appetite - is having its best month versus the U.S. dollar since April, in terms of percentage change.
The announcement damped a previously positive mood after reports that U.S. Senate Republican and Democrat leaders had agreed to resume negotiations on another coronavirus stimulus package.
On Wall Street, Pfizer Inc shares gained 0.78% after the drugmaker said its COVID-19 vaccine was 95% effective and the company would apply for emergency U.S. authorization within days.