Past diseases that have been declared as PHEIC are as follows:
Swine flu (2009–2010)
Zika virus (2016)
Kivu Ebola (2019–2020)
The outbreaks raise such concerns because they fit the definition and criteria of a PHEIC, posing as a threat to global health. This may due to the health consequences of the disease and its fatalities. For example, polio could cause permanent paralysis of the legs and arms, and to this day there is still no cure or specific treatment for it, which makes the disease very serious and dangerous. Meanwhile, Ebola has a very high case fatality rate of 50%. With the severe consequences of these diseases, it is understandable why they are listed as PHEIC. Another reason could be that the disease may overwhelm normal resources and capacities, leading to the interruption of essential health services. An obvious example with the COVID-19. In the early days of the pandemic, hospitals in many countries are completely flooded with COVID-19 patients, leading to a total collapse in the health system. Moreover, by listing a disease as a PHEIC, it could help direct global efforts into research of a cure or a vaccine to fight a novel pathogen. The COVID-19 vaccine was quickly developed even though it was a novel pathogen, thanks to global effort.
I think the next PHEIC would be a new type of infectious disease just like COVID. COVID-19 was a warning to how pathogens from different animal species could mix to form a deadly virus. The pandemic was a mix of multiple factors and failures. The origin of the virus, China, allowed the selling of exotic meats, and attempted to cover up the outbreak because of its political landscape. Other countries were slow to react, unprepared, and were slow to ban international travel. To this day, China has still yet to ban selling of exotic meat, and many countries in Asia still have the custom of eating exotic animals, which could mean that the exact same thing could happen again, mixing pathogens and eating of exotic animals leading to new diseases. Even in countries that do not have this custom, with global warming, many wildlife animals lose their habitat and are displaced. This could also lead to contacts between wild animals and the risk for new pathogens. Without substantial changes for prevention globally, the world is destined to repeat the same mistake.