Is an expansionary monetary policy effective against an exogenous negative growth shock?

If growth falls due to the usual causes ( overindebtedness , bursting of asset price bubbles), an expansionary monetary policy becomes necessary to make a high debt level acceptable, bolster asset prices and avert a banking crisis. But is an expansionary monetary policy also effective when growth falls because of an exogenous shock (such as the coronavirus crisis)? The answer is yes: debt sustainability and asset prices depend on the interest rate-growth differential ; i f the growth rate falls for an exogenous reason, the central bank must lower interest rates. This obviously creates a problem if risk-free interest rates and risk premia are already very low before growth falls. The central bank can also correct the liquidity crisis that may appear as a result of the fall in revenues by injecting more liquidity.