Stocks plowed higher on Wall Street Monday, as hopes for a COVID-19 treatment and vaccine had investors looking ahead to the possibility of a healthier economy that has shed the virus. The S&P 500 rallied 1 percent and added to the all-time high it set last week, when it erased the last of its losses from the coronavirus pandemic. It followed up on solid gains for stock markets across much of Europe and Asia. Hope was rising as pharmaceutical companies continue to work toward a possible vaccine for COVID-19 and after the US government on Sunday approved an emergency authorization to allow the use of convalescent plasma to treat patients. The plasma comes from patients who have recovered from the coronavirus, and it may help people battling the disease, though global health officials say the therapy is still experimental. Such hopes helped invigorate shares of industries that have been badly beaten down by pandemic life. Airlines climbed, for example, amid the possibility that people may feel safe enough to travel again in the future. Delta Air Lines rose 9.3 percent, and American Airlines Group added 10.5 percent.