There was an Ebola epidemic in 2014 and a Zika outbreak in 2016, but neither ended up becoming pandemic like the Spanish Influenza virus that killed up to 5 percent of the world's population (100 million people) in 1918. So, how does an outbreak turn into a pandemic? And how can we predict the next one?
A worldwide epidemic poses one of the greatest threats to humanity so – unsurprisingly – hundreds of scientists are currently attempting to predict when, where, and how the next one will start. But according to a new report published in Open Biology, this could be a waste of time. They "are likely to fail".
The problem is there are too many viruses, the researchers say. The evolution that has to take place for a pathogen to jump from an animal to a human (let alone from human to human) is so random and extraordinary that it's virtually impossible for current models to predict. Even if a virus achieves human-to-human transmission, several other factors are needed to cause a full-blown pandemic, like a relatively short incubation period and a dense population.
As of right now, we're aware of roughly 4,400 virus types. In reality, there are likely to be millions. Experts estimate that 99.9 percent of viruses are unknown but, luckily for us, most of these cannot be passed from animals to humans.
"The inconvenient truth... is that the vastness of the unknown virosphere and the diverse range of viruses that have achieved endemic transmission in humans means that any attempt to predict what virus may emerge next will face substantial, and probably crippling, difficulties," Australian scientists, Jemma Geoghegan and
They also point out that the two most recent epidemics have been caused by two well-described pathogens. Zika was discovered in 1947; Ebola in 1976. The greatest pandemic threat could lie in "viruses that re-emerge intermittently in large and dense host populations."
Geoghegan and Holmes aren't suggesting we sit back and wait for Mother Nature to do her thing. They promote a "more practical" approach, involving surveillance of geographical hotspots (places where humans and wild animals meet) for disease emergence. Instead of searching for viruses in animals, which they describe as a "Sisyphean exercise", we should focus on those found in humans.
"Humans are the best sentinels: a virus discovered in humans very obviously can replicate in that host, which will not be the case for myriad viruses identified through biodiversity surveys of other animal taxa," they wrote.
Many argue that the scientific efforts they critique shouldn't be so quickly dismissed. As Jonna Mazet, global director for PREDICT, told The Atlantic, had there been similar complaints in meteorology 100 years ago “we wouldn’t have created the data that lets us forecast the weather, which we can do pretty well now.”