Washington ? Fewer construction workers will be needed. Don’t expect as many interior designers or advertising copywriters, either. Retailers will get by with leaner staffs.

The economy is strengthening. But unlike in past recessions, jobs in the beleaguered manufacturing sector aren’t the only ones likely lost forever. What sets the Great Recession apart is the variety of jobs that may not return.

That helps explain why economists think it will take at least five years for the economy to regain the 8.2 million jobs wiped out by the recession — longer than in any other recovery since World War II.

Even as the economy strengthens, more Americans could face years out of work. The percentage of the labor force unemployed for six months or longer is 4.3 percent. That’s the highest rate on records dating to 1948.

Behind the trend are the cutbacks businesses made to make up for a loss of customers. They found ways to produce the same level of goods or services with fewer workers. Automation, global competition and technological efficiencies helped solidify the trend.

Diminished home equity and investment accounts have made shoppers more cautious, too. And their frugality could endure well into the recovery. That’s why fewer retail workers, among others, will likely be needed.

Among those whose former jobs may be gone for good are:

• Julie Weber of Milwaukee, who designed office cubicles for nearly seven years. She lost her job about a year ago. Since then, she’s been able to find only part-time work outside her field.

• Erik Proulx, 38, a former advertising copywriter in Boston, who finds more companies are turning to social media and viral marketing and are less drawn to agencies that focus on traditional TV and print ad campaigns. Proulx has started a blog to help other unemployed ad professionals network.

• Louis DiFilippo, 30, who decided to study information technology after losing his job managing a gourmet food store in Washington, D.C. After six months of unemployment, he now works on computer network security for the Navy.

More than one-third of chief financial officers at 620 big companies surveyed in March by Duke University and CFO magazine said they didn’t expect to restore their payrolls to pre-recession levels for at least three years. Nearly all cited higher productivity and tepid consumer spending.

Productivity grew at an annual rate of 6.3 percent in the year ending in March, the Labor Department said this month. It was the largest increase in 48 years, though most economists think that pace isn’t sustainable.

In the long run, more productive workers raise standards of living: Companies can pay more without inflating prices. But in the short run, high productivity delays hiring.

Many economists say eventually, companies won’t be able to squeeze any more work out of their employees. That would force employers to step up hiring.

But Janet Yellen, president of the Federal Reserve Bank of San Francisco, cautions that this won’t happen anytime soon. “We may be in store for … high productivity growth for some time,” she said in a speech this year. “If so, the rate of job creation will be frustratingly slow.”