Characteristics that Give Viruses Pandemic Potential

A handful of factors tip the scales in making a virus more likely to trigger a disruptive global outbreak. Right now, scientists tend to rank influenza, coronaviruses, and Nipah virus as the biggest threats.

Even before COVID-19 swept across the globe this year, coronaviruses were on scientists’ radar as pathogens that could one day ignite a pandemic. They’d threatened to before—in 2002–03, the SARS virus infected 8,000 people in more than two dozen countries and killed almost 800—and they checked off several specific boxes that emerging infectious disease specialists worry about in a virus. But they’re not the only group of viruses that researchers are concerned about. Influenza and a handful of other viruses have long been viewed as pandemic threats.

One aspect that signals pandemic potential in a virus is having an RNA, rather than DNA, genome. That’s because the process of copying RNA typically doesn’t include a proofreader like DNA replication does, and so RNA viruses have higher mutation rates than the DNA variety. “This means they can change and become more adaptable to human infection and human transmission,” says Steve Luby, an epidemiologist at Stanford University.

Researchers on the lookout for dangerous pathogens also pay close attention to viruses with track records of leaping from animals to people. Smallpox, measles, Ebola, and HIV all originated in animals, as Luby estimates that 80 percent of our most devastating infections did.

Once a virus makes the zoonotic leap from animals to humans, it must then transmit from one person to the next if it is to cause an epidemic. In this respect, SARS-CoV-2 seems to outperform the original and deadlier SARS coronavirus, MERS coronavirus, and some bird flu strains. But these less-transmissible viruses could always acquire some new mutation that revs up their R0, the expected number of infections caused by one person, increasing their potential to spread rapidly through human populations, saysRaina Plowright, an infectious disease researcher at Montana State University.

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