Similarly, a homeowner could be at risk of becoming a defendant if they failed to vaccinate their child against flu and the youngster passed on that illness to children invited for a play date–one of whom sickens and dies.

"The exposure is there [and] you've got a lawsuit on your hands," he warned.

Mr. Kutner said he thought malpractice actions could arise because of a lack of availability of flu vaccine, but he doubted they would be found to have merit.

There are also possible actions from medical complications arising from a flu shot, because "invariably there are complications from vaccines and lawsuits."

Employees, he said, can be encouraged to get flu shots, but, "Can you force employees to get flu shots? Probably not."

On the other hand, Mr. Kutner said that he believed an employer could be held liable "if you knew an employee was diagnosed with flu and you didn't tell everyone else on the staff."

To prevent against that sort of liability, he noted, universities make it a point to announce it to everyone at their institution when a student has contracted a communicable illness such as meningitis.

The key to a defense, he said, is putting third parties on notice when you have information. When a suit is brought, Mr. Kutner explained, the key issues are "What did you know? When did you know? And, what did you do about it."

In New York, Mr. Kutner noted there is a pending $40 million lawsuit brought by the family of school principal Mitchell Weiner against the city, claiming the Board of Education failed to alert the principal that he had been in contact with children who had tested positive for the virus; that it did not act quickly enough to stop the transmission of the disease; that it did not disseminate adequate information about health conditions that would increase the risks of the virus; and that it did not provide a safe working environment for Mr. Wiener and other school employees, among other allegations.

Mr. Kutner suggested that with so much exposure, insurers "are going to have to start thinking about homeowner policies and these big general liability policies."

"If there is a pandemic, it's potentially a major casualty loss," he said.