An unexplained onslaught of new flu strains could lead to a pandemic never seen since the deadly flu that hit the world in 1918, a recent study said. 

A study published in The Archives of Public Health on March 27 revealed that there had been a surge in the number of cases of flu strains infecting people since 1918 when a pandemic struck the world and killed an estimated 50 million people.

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The study was published by a team of researchers from the University of New South Wales. They found that there have been at least 19 separate strains discovered in the past century. Seven of which only showed up in the past five years.

With the emergence of fatal flu viruses, the researchers are calling for everyone to prepare for the possible coming of a big flu pandemic. The reason for the onslaught of new flu strains remains unclear, but the researchers are suggesting that climate change and urbanization are to be blamed.

"Some of the reasons involve things like climate change and its impact on pathogens, changes like urbanization, but none of these things have increased at the rate the virus is increasing so there's something else going on," one of the study authors said.

Sanjay Gupta, chief medicinal correspondent of CNN, said that in case the projection is true, people cannot solely rely on their immune systems. He suggested vaccines as the world's only real hope.

"That fact is part of the reason the number 24 has been stuck in my head the past few months as I have been working on the CNN original film 'Unseen Enemy,'" Gupta said while adding that a pandemic flu vaccine should be developed and deployed 24 weeks faster than currently projected.

Twenty-four weeks faster, he added, could mean the difference between 20,000 people dying in the next flu pandemic or more than 20 million people dying.