Italians start a widespread lockdown.

The circulation of a more contagious coronavirus variant, combined with a slow vaccine rollout, led to a 15 percent increase in cases nationally last week.

Three-quarters of Italians entered a strict lockdown on Monday, as the government put in place restrictive measures to fight the rise in infections.

A more contagious variant first identified in Britain, combined with a slow vaccine rollout, led to a 15 percent increase in cases in Italy last week, a worrisome picture for the government run by Prime Minister Mario Draghi.

“I am aware that today’s measures will have an impact on children’s education, on the economy but also on the psychological state of us all,” Mr. Draghi said on Friday. “But they are necessary to avoid a worsening that will make inevitable even more stringent measures.”

Most regions in northern Italy, as well as Lazio and Marche in central Italy and Campania and Puglia in the south, have shut schools and barred residents from leaving their homes except for work, health or necessity. Among business activities, only supermarkets, pharmacies and a few other stores will stay open, but restaurants are closed.

In the rest of the country, residents are not be allowed to leave their municipality without reason involving work, health or other necessities, but schools and many stores will stay open.