This paper discusses the effect of the number of people diagnosed with COVID-19 on market interest rates. Seven primary national currencies are analyzed, namely USD, GBP, RMB, AUD, TWD, EUR, and JPY. The effect of the new and total cases of diagnosis in the United States on the 1-month, 6-month, and 1-year fixed deposit interest rate of each national currency from January 1 to December 31, 2020 is examined. The trends and correlation between the monetary policies of the sampled nations, announced interest rate adjustment time, and the number of cases of diagnosis in the United States are analyzed. The effect of the number of cases of diagnosis in the United States on the market interest rate in each nation is investigated using a regression analysis. The results reveal a consistency between the time that the central banks cut the interest rates and the peak of new cases of diagnosis in the United States; that is, the number of cases of diagnosis in the United States significantly and negatively affects the interest rate of each national currency.