The coronavirus is weakening in Italy, several doctors say — but health authorities warn that 'this is still a killer virus'

• As the number of new daily coronavirus cases drops, Italy is relaxing its lockdown.
• One Italian doctor, Alberto Zangrillo, suggested on Sunday that the virus was weakening and had all but disappeared. "In reality," he said, "the virus clinically no longer exists in Italy."
• But an Italian health minister and other public-health experts said there was little evidence to back up that claim on a larger scale.
• "In terms of transmissibility, that has not changed. In terms of the severity, that has not changed," a World Health Organization expert said of the virus on Monday.

As daily coronavirus case numbers drop in Italy, some doctors have suggested that the virus is weakening and has all but disappeared in the country.

Alberto Zangrillo, who heads Milan's San Raffaele Hospital, told Italian TV on Sunday that "in reality, the virus clinically no longer exists in Italy," Reuters reported.

"The swabs that were performed over the last 10 days showed a viral load in quantitative terms that was absolutely infinitesimal compared to the ones carried out a month or two months ago," Zangrillo said.

But public-health authorities in Italy and at the World Health Organization have questioned the statements.

"Pending scientific evidence to support the thesis that the virus has disappeared ... I would invite those who say they are sure of it not to confuse Italians," Sandra Zampa, Italy's undersecretary of the health ministry, said in a statement, according to Reuters.

"We should instead invite Italians to maintain the maximum caution, maintain physical distancing, avoid large groups, to frequently wash their hands and to wear masks."

The virus' transmissibility and severity have 'not changed'

There could be an alternative explanation for Zangrillo's observation that Italian patients today have lower viral loads than patients did two months ago, when Italy was at the height of its outbreak.

A viral load refers to how much of a virus is present in a sample taken from a patient. Scientists still aren't sure whether higher viral loads correlate with more severe coronavirus cases. But two studies published in the journal The Lancet suggested that on average, people who developed more severe respiratory issues linked to COVID-19 had higher viral loads when they were first admitted to the hospital than people with mild cases.

"In a situation where the numbers of severe cases are falling, there may be time to start observing people with less severe symptoms — giving the impression that the virus is changing," Martin Hibberd, a professor at the London School of Hygiene and Tropical Medicine, told the Italian news site The Local.

In March, Italy's number of new cases confirmed each day hovered at about 6,500. The country's healthcare system was strained, so, in general, only patients with the most severe cases were admitted to the hospital. But at the end of May, the number of daily new cases had dropped to about 300. That may mean that more Italians — those with milder cases — were able to seek care, which could explain the lower viral loads in swab tests overall.

According to Maria van Kerkhove, the technical lead at WHO, the coronavirus continues to infect people at the same rate as when the pandemic started, and the same proportion of people — about 20% — develop severe cases.

"In terms of the transmissibility, that has not changed. In terms of the severity, that has not changed," she said during a press briefing on Monday.

'The strength the virus had 2 months ago is not the same strength it has today'

Matteo Bassetti, a doctor who heads the San Martino Hospital's infectious-diseases clinic in Genoa, said on Sunday that the coronavirus did not appear to be as lethal as it used to be.

"The strength the virus had two months ago is not the same strength it has today," Bassetti told an Italian news agency, adding that "it is clear that today the COVID-19 disease is different."

But according to Michael Ryan, the executive director of WHO's Health Emergencies Program, it's unlikely that the coronavirus mutated to become less dangerous.

"We need to be exceptionally careful not to create a sense that all of sudden the virus, by its own volition, has now decided to be less pathogenic," he said on Monday. "This is still a killer virus."

The coronavirus, like all viruses, does mutate over time, but those tiny changes in its genome don't necessarily affect how contagious it is or how severely it sickens people.

Both Ryan and van Kerkhove said it was possible that the virus is now less deadly because Italians are practicing social distancing.

"It may not be that the virus itself is becoming less potent," Ryan said. "It may be that we are — as community and as a global community — successfully reducing the number, intensity, and frequency of exposure to the virus, which, on the face of it, the virus then looks weaker."

Van Kerkhove added that measures that reduce and suppress transmission, including contact tracing and quarantining suspected cases, "reduce the potency and power of the virus."

This story has been updated to include statements from the World Health Organization and other experts. It was originally published on June 1 at 8:08 a.m. ET.