The Nikkei stock index extended gains in midmorning trading Tuesday, hitting its highest level in 31 years, as Japan's progress in vaccinating its population against COVID-19 fuels hope restrictions on economic activity will be eased. The 225-issue Nikkei Stock Average climbed above the 30,700 mark and approached 30,799.96, its highest intraday level seen on Aug. 2, 1990, when the Japanese economy was experiencing an asset-inflated bubble.
