What 11 Billion People Mean for Disease Outbreaks

The explosive growth of the human population—from 2.5 billion to 6 billion since the second half of the 20th century—may have already started changing how infectious diseases emerge

In mid-April 2009, samples from two California children suffering from the flu arrived at the Centers for Disease Control and Prevention in Atlanta for further investigation; something didn’t seem normal about the particular flu strains they had. Local clinics and flu surveillance staff had detected a virus that had a unique genetic makeup, different from any known human flu virus. It was entirely new to science.

That was the beginning of the 2009 swine flu pandemic. Countries around the world took notice and prepared for possible outbreaks, the World Health Organization sent out guidelines to ministries of health and vaccines were developed in a matter of months. The virus, which may have started infecting people first in Mexico, spread across the globe, infecting millions of people and killing thousands before running its course, with the pandemic coming to an end in August 2010.

The virus was a new strain of H1N1, the influenza virus involved in the devastating1918 Spanish flu pandemic, which killed between 30 million and 50 million people worldwide, according to the U.S. Department of Health and Human Services, more than died during World War I. The emergence of the new H1N1 in 2009 was a reminder that despite the unprecedented progress in treating infectious disease in the past decades, the looming shadow of a deadly pandemic still persists.

In fact, with every mysterious virus that surfaces, be it the 2009 swine flu, the 2002 SARS coronavirus, or most recently, MERS (Middle East Respiratory Syndrome, a viral respiratory illness that has emerged around the Arabian Peninsula and killed half of the people who have had it), the same questions come to the minds of researchers and health authorities: Is this the virus that’s going to cause the next pandemic? And will humanity be able to stop it?

And now, new challenges are being added to existing ones: The latest population projections from the United Nations, announced in a new report last summer, estimate that the world’s population will reach 9.6 billion people by mid-century, and 11 billion by 2100.

The sheer number of people, their interactions with animals and ecosystems, and the increase in international trade and travel are all factors that will likely change the way humanity deals with preventing and treating epidemics, experts say.

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