Mr. Trump spoke hours after the World Health Organization declared a global pandemic in hopes of spurring a more aggressive response, and on a day when infections in Europe jumped by almost a quarter from Tuesday to Wednesday, reaching more than 22,000.

Here are the latest updates on the virus and a map of where it has spread.

Notably, as leaders around the world grapple with the potential for crushing burdens on economies and health systems, Chancellor Angela Merkel of Germany said on Wednesday that two in three people in her country might become infected. India also joined a growing number of countries that have imposed drastic travel limits.

But so far, our London bureau chief writes in an analysis, the global response is “less a choir than a cacophony.” He says that is partly — though not entirely — because Mr. Trump has ignored scientific advice and has failed to work with world leaders to fashion a common response.

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