The World Health Organization is creating an updated list of the globe’s most dangerous microbes. The public health agency will recruit over 300 scientists to work on the list. They will consider known germs across dozens of virus and bacteria families. One automatic inclusion will be “Disease X,” the moniker given to a currently unknown pathogen capable of causing the next pandemic.

The WHO’s list of priority pathogens, as they call it, was first drafted in 2017 and the last major assessment of it happened in 2018. The list is meant to identify pathogens that need urgent attention because of their potential to cause large epidemics and/or because there are few options available to combat them, should they ever become major problems. This information is then used by the WHO and others to help decide where to direct funding into researching new vaccines, tests, and treatments.

“Targeting priority pathogens and virus families for research and development of countermeasures is essential for a fast and effective epidemic and pandemic response. Without significant R&D investments prior to the covid-19 pandemic, it would not have been possible to have safe and effective vaccines developed in record time,” said Michael Ryan, executive director of WHO’s Health Emergencies Programme, in a statement released Monday.

While SARS-CoV-2 was unknown to scientists until the covid-19 pandemic it caused began in late 2019, the WHO’s list did and still does include the coronaviruses behind Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS). The covid-19 virus has since been added to the list, and other germs currently on it are those responsible for causing Crimean-Congo haemorrhagic fever, Ebola, Marburg, Nipah and similar viral diseases, Rift Valley Fever, Zika, and Lassa. “Disease X” is intended to represent the possibility of a previously undiscovered germ causing human illness on a large scale.

“This list of priority pathogens has become a reference point for the research community on where to focus energies to manage the next threat,” said Soumya Swaminathan, WHO chief scientist, in a statement. “It is developed together with experts in the field, and is the agreed direction for where we—as a global research community—need to invest energy and funds to develop tests, treatments and vaccines.”

This time around, scientists will be asked to adopt a broader approach to identifying potential threats, one that will focus more on families of pathogens rather than individual germs—a change inspired by the lessons learned from the covid-19 pandemic, according to the WHO. All in all, over 300 scientists are expected to weigh in on the selections and review evidence concerning pathogens across 25 families of viruses and bacteria. The deliberation process began last week, and the WHO is expected to release the list sometime early next year.