A flu virus that health officials have called "the mother of all pandemics" has resurfaced for the first time in nearly a century - in a lab. Now experts are questioning the wisdom of bringing something so deadly back into the world.

According to the United States Centers for Disease Control and Prevention (CDC), the Spanish flu managed to infect nearly a third of the Earth's recorded population in 1918, killing an estimated 50 million people with many more suspected deaths gone unrecorded.

Interestingly, while most influenza viruses target the sick and the elderly, this virus had no qualms infecting young and healthy men and women around the world, a CDC report says.

To finally address many burning questions, researchers from the University of Wisconsin at Madison and the University of Cambridge have led an international team in essentially re-creating the Spanish flu in a controlled lab setting.

According to a study published in the journal Cell Host and Microbe, the researchers managed to create an influenza virus with a mere 3 percent difference from the strain that swept across the world in 1918.

 "This is information for those making decisions about surveillance and pandemic preparedness... have real world applications," researcher Yoshihiro Kawaoka explained to the Washington Post.

He noted that the virus is being studied in a "highly regulated" environment, and there is no chance it could ever reach the general public.

But other scientists are skeptical. Marc Lisitch and Alison Galvani, from Harvard and Yale respectively, speak on behalf of the vocal sector of the scientific community that believes reviving deadly and dangerous pathogens purely for scientific study is far too risky.

According to an article written by the epidemiologists, if 10 "highly regulated" labs in the United States performed experiments for 10 years, the chance of at least one researcher becoming infected is almost 20 percent. The chances of that person ever getting to leave the lab are slim, but the possibility remains.

The article suggests that potential pandemic pathogens (PPP) research, like Kawaoka's, "would pose substantial risks to human life, even optimistically assuming a low probability that a pandemic would ensue from a laboratory accident."

"We are not saying this is going to happen, but when the potential is a pandemic, even a small chance is something you have to weigh very heavily," Marc Lisitch, from the Harvard School of Public Health, told The Guardian.

The flu study was published in Cell Host and Microbe on June 11.

The critical article was published in PLOS Medicine on May 20.