“There’s a race right now between these variants of concern and vaccines,” she said during a webcast event Tuesday. She urged “global cooperation and attention” to how disparities in vaccine distribution affect inequality and economic recoveries.

The I.M.F. agrees. Vitor Gaspar, the fund’s director of fiscal affairs, said that advanced economies would continue to be at risk even if the virus were raging in developing countries that are not major economic powers, noting that the virus cannot be eradicated anywhere until it is eradicated everywhere. For that reason, he said, investing in vaccinations is critical.

“Global vaccination is probably the global public investment with the highest return ever considered,” Mr. Gaspar said in an interview. “Vaccination policy is economic policy.”

While global policy bodies are warning about diverging growth and public health outcomes, some Wall Street economists have taken a more optimistic tone.

“We think market participants underestimate the likely pace of improvement in both the public health situation and economic activity in the remainder of 2021,” Jan Hatzius at Goldman Sachs wrote in an April 5 research note.

Vaccinations are high or progressing in Canada, Australia, Britain and the euro area. In emerging markets, Mr. Hatzius wrote, Goldman economists expect 60 to 70 percent of the population to have “at least some immunity” by the end of the year when counting prior coronavirus infection and vaccine proliferation.

“The laggards are China and other Asian countries, although this is mainly because Asia has been so successful in virus control,” he wrote.

How fast global recoveries proceed could be critical to the policy outlook, both in government support spending and in central bank monetary help.

From the Fed to the European Central Bank and Bank of Japan, monetary authorities have employed a mix of rock-bottom rates, huge bond purchases and other emergency settings to try to cushion the pandemic’s fallout.

Organizing bodies have echoed Ms. Yellen’s comment: They argue that it’s important to see the recovery through, rather than pulling back on economic help early.

Global policymakers “generally view the risks to financial stability associated with early withdrawal of support measures as currently greater than those associated with a late withdrawal,” Randal K. Quarles, the Federal Reserve’s vice chair for supervision and head of the global Financial Stability Board, said in a letter released Tuesday.

The I.M.F. said on Tuesday that it was keeping a close eye on interest rates in the United States, which could pose financial risks if the Fed raises them unexpectedly. It also urged countries to maintain targeted fiscal support — and to be ready to provide more if future waves of the virus emerge.

“For all countries, we’re not out of the woods, and the pandemic is not over,” said Gita Gopinath, the I.M.F.’s chief economist.

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