Covid-19 Live Updates: Trump Administration Vaccine Chief Casts Doubt on Vaccine by Election Day

But, she added, school was probably as safe as any place to be as a child was just as likely to catch Covid-19 at a family weekend gathering, or while out in the park.

“We don’t know, because the virus is everywhere,” she told esRadio. Ms. Díaz Ayuso did not say what scientific evidence she used to predict that the infection rate would be so high among children.

Madrid is once more the epicenter of Spain’s virus pandemic, accounting for almost one quarter of the 1,830 patients hospitalized in the country in the past week.

In response, Madrid is now requiring testing of all teachers returning to school, as is the case in other regions.

The result on Wednesday was chaotic: huge queues of school staff outside packed test centers forced the testing process to be suspended.

As the situation worsens in Madrid, some other regional leaders have been voicing their concerns about allowing residents from the capital region into their towns.

But Salvador Illa, Spain’s health minister, on Thursday ruled out the idea of imposing a lockdown around the Madrid area.

In other developments from around the world:

• Thailand has gone 100 days without a reported case of local transmission, but its success in halting the spread of the virus has come at a significant financial cost. Thailand’s last reported case of community transmission was confirmed on May 24. Hundreds of cases have been found since then among residents returning from abroad, but all were detected during the required 14-day quarantine periods. As of Thursday, Thailand had reported 3,425 cases and 58 deaths, according to a Times database.

• India reported 83,883 new cases on Thursday, breaking its own global record. It has the third-highest number of cases and deaths after the United States and Brazil.

• The Czech Republic reported 650 new cases on Thursday, its highest single-day increase.

• Turkey will impose restrictions on weddings and other social events amid a surge in new cases. The daily number of cases has reached almost 1,600 in the last week.

Reporting was contributed by Liz Alderman, Ilise S. Carter, Choe Sang-Hun, Patricia Cohen, Ben Casselman, Michael Gold, Christina Goldbaum, Kathleen Gray, Luis Ferré-Sadurní, Jacey Fortin, Ethan Hauser, Jennifer Jett, Juliana Kim, Isabella Kwai, Sharon LaFraniere, Raphael Minder, Matt Phillips, Campbell Robertson, Amanda Rosa, Eleanor Stanford, Jim Tankersley, Katie Thomas, Lucy Tompkins, Neil Vigdor, Allyson Waller, Lauren Wolfe, Katherine J. Wu and Carl Zimmer.