It forecasts the outbreak will cut US economic output by 3% between this year and 2030, a loss of $7.9tn (£6.3tn).
The warning comes as tens of millions of people are out of work due to lockdown measures.
America's historic downturn comes even after trillions of dollars have been pumped into the economy.
The nonpartisan CBO said the majority of the loss was caused by the sharp contraction in economic activity this year, which it had not predicted in its last 10-year report, published in January.
