A box fan, an air filter — and duct tape to attach them. With four such devices cobbled together for a grand total of about $150, the vice-presidential debate on Wednesday night can be made much safer than with the plexiglass barriers being used, according to experts in airborne viruses.

Vice President Mike Pence and Senator Kamala Harris will be seated more than 12 feet apart, with barriers between them. But the barriers will do nothing to protect Ms. Harris if Mr. Pence is infected and exhaling virus that can be carried through the air, experts said.

On Monday, the Centers for Disease Control and Prevention released new guidelines indicating that indoors, the virus can be carried aloft by aerosols — tiny droplets — farther than six feet. In one study in August, scientists found infectious virus at a distance of 16 feet from an infected patient.

Linsey Marr, an