A study at the University of Edinburgh has identified 37 viruses with the potential to cause major epidemics worldwide. All 37 have displayed transmission in humans, but have not yet caused large outbreaks of disease in the contexts in which they exist.
The viruses identified by the study were all zoonotic in nature, meaning that their transmission is largely limited to certain animals. The study's approach to the viruses was to assign to viruses one of four levels of significance to humans, corresponding each to human exposure to the virus, the incidence of infection once exposed, the potential for transmission given infection incidence, and then the potential for blow-up into a full-scale epidemic. Some viral families, like avian flus, are able to 'skip' some levels, jumping straight from exposure to human-human transmission, for example. Other, more slowly evolving viruses, may make contact with humans but, for their inability to become infective, were discounted as risks in the study.
Other parameters used to evaluate viral risk were the relatedness of virus reservoir hosts to humans, which led to a prioritization of primate viral families, viral host range, host restriction factors and host-virus coevolution. Virulence was also included both as a factor which increases the significance of viral disease, and the potential cost of a pandemic, but which also limits the ability of a virus' hosts to survive long enough to infect a great number of people.
The method of the study was previously used to report the threat of the Ebola virus strain involved in the 2014 outbreak, as well as the threat presented by the Zika virus. Despite this, the identification of the dangers these viruses posed did little to spur early precautionary measures and international coordination to monitor and respond to outbreaks of disease. While this research is certainly valuable for the understanding of the viral risks which exist, whether this value is realized depends on the ability of the international community to find ways to make practical the findings it reports.