ROME — Silvio Berlusconi’s doctor says that the hospitalized former Italian premier is responding “optimally” to COVID-19 treatment, but that he belongs to the most vulnerable category of patients and is in “the most delicate phase” of the virus.

Dr. Alberto Zangrillo, who is head of intensive care at the San Raffaele hospital in Milan, repeated Sunday that he nevertheless remained “cautiously optimistic” about Berlusconi’s recovery.

“The patient is responding optimally to treatment," he said. "This doesn’t mean we can claim victory because, as you know, he belongs to the most fragile category” given his age. He also suggested Berlusconi would not be released anytime soon, recalling that the virus “requires adequate treatment and takes its time.”

The three-time premier turns 84 in a few weeks and has had a history of heart problems that required being fitted with a pacemaker several years ago. He checked into San Raffaele Friday after testing positive for the virus earlier in the week. Zangrillo said at the time that he had the early stages of a lung infection.

Data from Italy’s Superior Institute of Health indicates men aged 80-87 have the highest COVID-19 lethality rate among all cases in Italy, at 47%.

Berlusconi spent some of his summer vacation at his seaside villa on Sardinia’s Emerald Coast. Many of Italy’s recent cases of COVID-19 have been linked to clusters in people who vacationed on Sardinia.