There's a difference in time scales. In the short run, while everything is locked down, there's been a near total destruction of demand and (generally) a fall

There's a difference in time scales. In the short run, while everything is locked down, there's been a near total destruction of demand and (generally) a fall in prices. Businesses are not making any revenue, they can't afford to pay workers, the workers are being laid off, and nobody can afford to buy anything even if they were allowed to go outside anyway. That's deflationary. The Fed's monetary policy response has been to pull out all the stops to reverse that. There'll be trillions of dollars injected directly into the economy within the next month. The problem comes when lockdown ends and people start buying things and going out again. That should be right around when the supply chain impacts of the virus hit (there's usually about 1-2 quarters worth of product buffered in various stages of the supply chain). High demand + low supply + basically free money = lots of inflation. It's also hard to eliminate inflation from the economy once it starts, because the Fed's primary tool is interest rates and you have to get ahead of the inflation rate. The real interest rate = nominal rates - inflation, so if inflation is running at 20%, then to raise real interest rates to just 10%, you need nominal rates of 30%. Particularly if inflationary expectations are increasing, your policy tools may not be sufficient to temper those expectations.