It took one week after the first U.S. case of COVID-19 with no overseas connection for Starbucks Corp. to temporarily ban customers from bringing in reusable coffee mugs.

Judith Enck, a former regional administrator for the Environmental Protection Agency, was disappointed. Public health comes first, of course, but as the founder of the grassroots Beyond Plastics project, Enck had her doubts that returning to disposable cups would make anyone safer. Currency, for instance, is a notorious germ-carrier. "Will Starbucks now stop accepting cash?" she says.

These are nervous times for activists working to wean the world off plastics. Until the novel coronavirus started its spread across the globe, 2020 appeared to be a year when meaningful plastic-use restrictions would finally take hold. A growing list of consumer companies—including Coca-Cola Co., which produces about 117 billion plastic bottles each year—had set targets to reduce their reliance on plastic packaging. France prohibited single-use plastic plates, cups and cutlery starting Jan. 1, and England will enact restrictions on plastic straws and stirrers starting in April. On March 1, New York joined a number of other cities around the world in banning the distribution of plastic shopping bags by retailers.