The Bank of Japan’s most anticipated policy announcement in years left investors underwhelmed, sparking a surge in the yen and sending government bonds and emerging-market stocks lower. Japan’s currency rallied against all of its 31 major peers after the BOJ kept its government-bond buying target and policy interest rate unchanged, opting instead to increase exchange-traded fund purchases.

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The P4 laboratory, on the campus of the Wuhan Institute of Virology, in Wuhan, in China's central Hubei province. (Hector Retamal/AFP via Getty Images)