U.S. stocks fell on Monday, while Treasury yields rose after ratings agency Moody's downgraded the country's sovereign rating by one notch, bringing forward concerns around the ballooning U.S. debt.

Moody’s on Friday after the bell bumped the country’s rating down by one notch to Aa1 from Aaa, bringing the agency in line with its peers. The firm cited the financing challenges tied to the federal government’s growing budget deficit and the ramifications of rolling over existing U.S. debts in a period of high borrowing costs.

The debt downgrade pressured bond prices, sending yields higher, at a time when the economy is already under pressure from President Donald Trump’s unfolding tariff policy. The 30-year U.S. bond yield traded above 5% on Monday and the 10-year yield topped 4.5%, levels that pressured equity markets last month and helped cause Trump to back off his stiffest tariffs. Loans for houses, cars and credit cards track these rates.

Novavax shares surged 20% on Monday, following the long-delayed approval of its COVID-19 vaccine from the U.S. health regulator, albeit with new conditions.