LONDON—The dollar rose against major rival currencies in holiday-thinned trading on Thursday, as investors remained cautiously optimistic about the economic consequences of a surge in cases of the Omicron coronavirus variant. Reuters data shows global COVID-19 infections hit a record high over the past seven days but, comforted by data suggesting the virus may turn out to be milder than in previous waves, many governments have resisted imposing widespread new lockdowns. The dollar index, which measures the greenback against major peers, rose 0.39 percent to 96.19 after the S&P 500 and the Dow Jones Industrial Average stock indexes closed at all-time highs on Wednesday, the latter rising for a sixth session. “There’s definitely cautious optimism around, though the dollar is mostly just recovering the ground it lost yesterday afternoon (after the trade data) rather than anything more substantial,” said Kit Juckes, head of FX strategy at Societe Generale in London. …