Psychological fatigue with social distancing is emerging as a major challenge for curbing a pandemic now into its eight month. That's especially so among young adults who are less fearful of the corona­virus and who suffer greater economic and social costs when they stay home.

From Japan to Spain and the United States, infections among millennials and Generation Z are driving new waves of cases that don't seem to be abating despite reimposed restrictions. The worrying trend reflects that social distancing curbs are proving untenable over a long period, despite their initial efficacy in flattening the virus curve across the world earlier this year.

"They are the people who are most economically and socially affected with lockdowns but who are least affected by the disease," said Peter Collignon, a professor of clinical medicine at the Australian National University Medical School in Canberra, "The problem we've got is people we most need to change their behavior are the 20- and 30-year-olds."

The fact that younger people are less at risk for a severe COVID-19 infection or death has emboldened them to breach the rules as job losses mount. Young adults are stepping out for reasons that range from commuting for work or caregiving, to visiting bars and nightclubs and even disturbing instances of COVID-19 parties to deliberately get infected.

For governments facing aggressive resurgences and an effective vaccine still months away, there are few options besides the plea to stay home.

"How do you maintain behavior in that group?" Collignon said, "That's a dilemma that I don't know the answer to."