The other day at a Starbucks in New York, Norma Siciliano was sitting near a young man sipping a latte who let out a loud sneeze — and, no, he did not cover his nose or mouth. When another man sitting nearby told him to be more considerate and stay home, a volley of curses ensued.

Already, people are feeling “outrage on a lot of levels,” says Siciliano, who runs a telemarketing consulting business in New York. “I think we’re going to see a lot more of this.”

If anything, the flu vaccine shortage may heighten concerns about infectious people — including those who soldier into work while sick — and what could develop into full-blown flu rage.

In the past, even the most uncompassionate may have had sympathy for such die-hards who drag themselves out despite the bleary eyes and body aches.

But this year workers are feeling more vulnerable, said Richard A. Chaifetz, chief executive of ComPsych, a Chicago provider of employee assistance programs.

“It’s not a paranoid feeling,” he said. “It’s based in reality.”

It’s no wonder. Sixty percent of employers polled by the Society for Human Resource Management in Alexandria, Va., had planned to offer flu shots this year. But most of those plans have been scrapped because of the vaccine shortage. The upshot: as much as $20 billion in lost productivity, said David Cutler, a health economist at Harvard University.

And the loss from “presenteeism” — sick workers who come in anyway, only to get less done and infect co-workers — could be even worse. Add those in, and presenteeism may account for more than half the cost attributed to worker illnesses, according to a study by Cornell University and Medstat, a Michigan-based health information company.