Chubb Ltd. posted a net loss for the second quarter, mainly due to COVID-19 losses, and its top executive warned Wednesday that pandemics are uninsurable on a broad basis without the federal government playing a major role.

Chairman and CEO Evan Greenberg said COVID-19 is a “slow-rolling global catastrophe” with no geographic or time limits and that it affects both sides of the balance sheet.

Chubb on Tuesday reported a net loss of $331 million for the second quarter, compared with net income of $1.15 billion in the same period of 2019.

As previously announced, Chubb’s net catastrophe losses of $1.51 billion included $1.16 billion of COVID-19 pandemic losses, $353 million in civil unrest losses and other natural catastrophe losses.

Chubb also saw unfavorable prior-year reserve development of $52 million after-tax, including $205 million for U.S. child molestation claims, the vast majority reviver statute-related, it said.

On a conference call Wednesday, Mr. Greenberg cautioned that the COVID-19 loss is Chubb’s best estimate of the ultimate loss on its balance sheet and its liabilities from the pandemic.

“Did we get it precisely right? God knows. Is there risk around it? Of course, there is. Because you tell me what the next six or nine months precisely is going to look like? No one knows. There’s great uncertainty,” Mr. Greenberg said during the call.

Chubb’s property/casualty combined ratio for the second quarter was 112.3%, compared with 90.1% in the same period of 2019.

Frequency and severity in most lines of business are benefiting because commercial activities are down, Mr. Greenberg said.

While shrinking economic activity is having a negative impact on growth, Chubb is benefiting from favorable commercial property/casualty underwriting conditions.

“We expect Chubb will have positive premium revenue growth for the full year,” Mr. Greenberg said.

Net premiums written in the second quarter, at $8.36 billion, were up 0.1%, while property/casualty net premiums written were $7.74 billion, down 0.4%, Chubb said.

Net premiums written were reduced by $191 million to reflect exposure adjustments on Chubb’s in-force policies due to COVID-19, it said.

“In those markets where we grew, we improved rate to exposure across most all commercial product lines,” Mr. Greenberg said.

Overall rates in North American commercial P/C increased by 14%, and in major accounts and specialty, rates for property were up 21%. Casualty rates were up more than 25.5%, and financial lines rates were up over 18.5%.

Middle-market business property rates were up 18%; casualty rates were up over 12%, excluding workers compensation. Workers compensation rates were down 1%, and financial lines rates were up 14.5% for middle-market business.

In Chubb’s international general insurance operations, rates were up 16% in international retail business and 20% in London wholesale.

During the call Mr. Greenberg also hit out at attempts by the trial bar to “conjure up business interruption coverage that for the most part doesn’t exist.”

“Coverage for pandemic was never contemplated in standard business interruption policies, and therefore no premiums were ever charged for those risks,” he said.

However, the industry has an important role to play in a prospective pandemic risk solution, he said. Chubb recently put forward its own government-backed risk-sharing pandemic plan.

Chubb is also an active supporter of Republican efforts to provide a safe harbor for businesses to mitigate future liability claims related to the pandemic, Mr. Greenberg said.

To foist on businesses the burden of liability is “an additional expense which ultimately benefits one industry — the trial bar — would be a travesty and a shame,” he said.

For the first half of 2020, Chubb swung to a net loss of $79 million, compared with net income of $2.19 billion for the same period of 2019.

The P/C combined ratio deteriorated to 101% for the first half, compared with 89.6% for the same period of 2019.

More insurance and risk management news on the coronavirus crisis here.