They walk among us, dead-eyed, with heavy tread. They are the colleague sagging at the coffee machine, the project manager staring out of the window. Meet the zombie workforce: an army of employees who’re failing to find inspiration at work.

There are more of these “working dead” than you might imagine. According to a recent study by Aon Hewitt, less than one-quarter of the world’s employees are classified as “highly” engaged in their jobs, while only 39% admit to being “moderately” so.

This leaves an awful lot of the 5 million people Aon surveyed "unengaged", which the more gruesome-minded of us might take to mean "haunting office corridors like reanimated corpses" where once they might have been valuable staff members, full of life and great ideas.

Why does this matter?

Well quite apart from the human tragedy of employees spending eight hours a day feeling unfulfilled, disengagement among workers seeps out to infect society at large. When engagement levels among employees are low, businesses report a higher turnover of staff, more absenteeism and lower customer satisfaction.

Zombie workers cost US businesses $550 billion a year, according to Gallup.

The wider economic ramifications of this are easy to anticipate: weakness in the business sector leads to a decline in national prosperity, and with that comes a drop in people’s collective living standards.

It’s all to do with competitiveness, explains an economist at the World Economic Forum, Xavier Sala-I Martin. “Nations that are more competitive are more productive, and are therefore more able to provide for the social needs of their people,” he says.

In short: engagement leads to productivity, which leads to prosperity – and this leads to a fairer, happier societies.

So, what’s sapping workers of their vitality?

One global trend appears to be a growing anxiety caused by the changing nature of jobs and the rise of machines. As Ken Oehler of Aon Hewitt told the website HR Drive: “Along with rapid advances in technology that are increasingly threatening job security, fewer employees are engaged, and we expect this trend to continue.”

Other forms of change are equally unsettling: travel bans and other migration restrictions create uncertainty as the professional world braces for changes in its talent pipelines and workers can’t travel abroad towards the jobs they trained for.

There’s also a lack of proper on-the-job training. Organizations are struggling to skill, re-skill and up-skill their staff as roles change, contracts shorten and traditional CV credentials become outdated.

Then there’s workers’ rights – or more specifically, the alarming lack of them. It’s hardly surprising that employee enthusiasm has dimmed in the face of stagnating wages and rampant job insecurity. Flexibility may be the future, but it’s widely agreed now that this shouldn’t come at the cost of economic stability.

“Competitiveness is enhanced, not weakened, by combining degrees of flexibility within the labour force with adequate protection of workers’ rights,” says Alain Dehaze, CEO of Adecco, one of the world’s largest staffing companies.

But the zombie apocalypse is far from guaranteed. The world might only be nurturing a small percentage of its workers – only 62% are gainfully developed, according to a recent report on human capital – but employees need not be hapless victims.

In fact, if you're feeling a little braindead at work yourself, there are several actions you can take to find and hold on to a job you can love. According to Stephane Kasriel, CEO of Upwork, the trick is to give yourself a firm assessment. “Ask yourself: are my skills still in demand? What’s the outlook for them? What skills could I work on today that would increase my income potential in the coming years?

“Do this exercise every few years. If the half-life of a job skill is about five years, you want to get ahead of that decline in value.”

What's the lesson in all of this? A lifelong learner is a living learner. Remember that and you may just survive.