Russia confirmed 302 new coronavirus infections on Monday, bringing the country’s official number of cases up to 1,836, with nine deaths. Moscow accounted for 212 of the new cases and 1,226 of infections overall.

Young people make up a majority of Moscow’s new Covid-19 patients, the city’s coronavirus crisis center said Monday as Russia set another one-day record in new cases of the deadly disease.

Out of Moscow’s 212 new cases, 102 patients (48%) are residents aged 18 to 40, the Russian capital’s crisis center said.

Another 17 patients (8%) are children, meaning 56% of Moscow’s new coronavirus cases are younger than 40 years old.

Of the remaining 93 new coronavirus patients, 58 are between 40 and 65 years old and 35 are older than 65, the crisis center said.

In a separate statement, the crisis center said that 45% of Moscow's patients in serious condition are younger than 60 years old. Nearly 40% of patients younger than 40 years old are on respirators, it added.

The data challenges studies that have said the virus most severely affects the elderly and people with underlying medical conditions. Some 10% to 15% of patients under the age of 50 have moderate to severe infection, according to Dr. Mike Ryan, the World Health Organization’s top emergencies expert, a percentage he called a “significant minority.”

Moscow introduced an indefinite quarantine for all residents starting Monday, enforced by a “smart monitoring” system that observers say will employ the city’s vast network of facial-recognition cameras, after initally only ordering residents over 65 to self-isolate.

Russia’s prime minister, who had closed national land and maritime borders a day earlier, has asked Russia’s other regions to enact similar lockdown measures.

President Vladimir Putin declared this week to be a nationwide paid “non-working” week in an effort to encourage Russians to stay home and slow the spread of the pandemic that has infected more than 720,000 people and killed more than 33,000 worldwide.

Moscow Mayor Sergei Sobyanin, Putin’s close ally, said 20% of residents were ignoring his order to self-isolate.

Reuters contributed reporting to this article.