Gainers on Monday included Johnson & Johnson, which said it had identified a lead candidate for a vaccine for the virus and planned to ramp up both production and clinical testing. Abbott Laboratories rose on reports that it had said a new test that could detect the virus in five minutes had been cleared for use by the Food and Drug Administration.

But there were lingering signs of caution in the financial markets. Most notably, oil prices tumbled to their lowest levels since 2002.

And in the stock market, Monday’s rally came on relatively light volume, said Matt Maley, chief market strategist at Miller Tabak, a trading and asset management firm. That suggests a lack of conviction among investors, he said.

“It’s a little bit of lack of confidence,” said Mr. Maley, “And you can’t blame them after what’s happened.”

Some industries continued to be battered by the long shadow of the virus. Cruise lines Royal Caribbean, Norwegian and Carnival were all down 10 percent, making them some of the worst performers in the S&P 500 on Monday. United Airlines, American Airlines and Boeing, all of which had rallied last week on expectations that they would benefit from government assistance, also fell sharply.

The dizzying moves that characterized trading in financial markets for most of March seem to have ended as policymakers around the world moved to bolster their economies with spending and other means of support. But investors were weighing those efforts against the rising number of coronavirus cases and the redoubled efforts to contain the pandemic.