The director general of the World Health Organization (WHO) recently urged countries across the globe to prepare for the next pandemic, warning that future health emergencies could be even worse than the COVID-19 pandemic.1 SARS-CoV-2, with the omicron variant XBB fueled a resurgence in China, variant EG.5 has recently been the most prevalent in United States (approximately 20%), and a new more virulent variant BA.2.86 has very recently been detected in at least 5 countries in the month of August (2023), which has potential to cause breakthrough infections, according to the Centers for Disease Control and Prevention. The damage the COVID-19 pandemic caused raised awareness of the ever-present threat of a new epidemic and the possibility of it turning into a new pandemic. Of the 5 pandemic events since 1900, all have been linked to either influenza or a coronavirus.2 The WHO developed a list of pathogens with pandemic potential. This list gets updated once a year by a group of over 300 scientists, who weigh up a pathogen's transmissibility and the treatment options available. At present, the priority diseases are COVID-19, Crimean-Congo hemorrhagic fever, Ebola virus disease, Marburg virus disease, Lassa fever, Middle East respiratory syndrome coronavirus (MERS-CoV), severe acute respiratory syndrome (SARS), Nipah and henipaviral diseases, Rift Valley fever, Zika disease, and Disease X.3

The WHO has binding rules known as the International Health Regulations, which in 2005 set out countries' obligations where public health events have the potential to cross borders. A treaty for future pandemic preparedness has been proposed by the world leaders.4

SOURCES OF THE DISEASES

Coronaviruses are common in bats, which make up 20% of all mammal species and can easily spill over to other mammals such as cats, civets, deer, dogs, and mink.5 Crimean-Congo hemorrhagic fever is caused by a tick-borne virus Nairovirus. Ixodid (hard) ticks are both a reservoir and a vector for the CCHF virus. For Ebola virus and Marburg virus, bats are reservoir hosts. Lassa fever virus is spread by rats. MERS-CoV and SARS are thought to have originated in bats. MERS-CoV was passed to camels. SARS-CoV infected palm civets. Nipah and henipaviral diseases' primary reservoirs are bats. Pigs and horses could be intermediate hosts. Rift Valley fever is a zoonotic mosquito-borne disease. It is commonly seen in domesticated animals, such as cattle, buffalo, sheep, goats, and camels. Zika is transmitted by mosquito.

DISEASE X

Disease X is a hypothetical, unknown pathogen that could cause a future epidemic.6 This is a placeholder name for an “unknown” pathogen. History tells us that it is likely that the next big outbreak will be something we have not seen before.7 In 2020, The Lancet Infectious Diseases published an article titled “Disease X: accelerating the development of medical countermeasures for the next pandemic,” which included the term Pathogen X that causes Disease X and identified areas of product development and international coordination that would help in combatting any future pandemic.8 There are speculations about the source of Disease X; it could come from zoonotic transmission, an animal virus that gets transmitted to humans, or due to leak from a laboratory where Disease X pathogen could be intentionally created as a biological weapon, for example, production of synthetic viruses using gene-editing technology.9 Virologists suggested that RNA viruses should be treated as the main pathogen of pandemic potential, because they lack good autocorrection system in their genetics, so they have more chance to mutate than DNA viruses.10

It is known that some microbes have higher pandemic potential. Besides viruses, other microbes such as fungi and bacteria have possibility to cause a major disease outbreak. Also, increasing antibiotic resistance of bacteria could turn into a potential Disease X.11

It has been found that a high level of population immunity, including natural immunity, immunity due to infection, and immunity due to vaccine, has an impact on reducing severe illness and mortality caused by COVID-19.12 To control the spread of future infectious diseases, a foundation called the Coalition for Epidemic Preparedness Innovations (CEPI) focuses on the WHO's priority diseases, it finances research projects to develop vaccines against emerging infectious diseases.13 CEPI investments in pharmaceutical companies require equitable access to the vaccines during outbreaks. CEPI's goal is to make vaccines affordable and available.

Because of the greater intensity of animal and human contact, threats of Disease X remain high; however, the world is better equipped compared with the situation in 2019. Scientists say the infectious diseases do not obey regional boundary, so no one is safe until everyone is safe.

REFERENCES 1. United Nations. WHO director-General's report to member states at the 76th world health assembly. 2023. Available at: https://news.un.org/en/story/2023/05/1136912. Accessed May 22, 2023. 2. Looi MK. What could the next pandemic be? BMJ. 2023;381:909. 3. World Health Organization. Prioritizing diseases for research and development in emergency contexts. Available at: www.who.int/activities/prioritizing-diseases-for-research-and-development-in-emergency-contexts. Accessed March 20, 2020. 4. UK Parliament. House of commons library: what is proposed WHO pandemic preparedness treaty? 2023. Available at: https://commonslibrary.parliament.uk/research-briefings/cbp-9550. Accessed June 2, 2023. 5. Dyer O. Covid-19: Denmark to kill 17 million minks over mutation that could undermine vaccine effort. BMJ. 2020;371:m4338. 6. World Health Organization. List of blueprint priority diseases. February 7, 2018. Archived from the original. Available at: http://origin.who.int/blueprint/priority-diseases/en/. Accessed March 20, 2020. 7. World Health Organization. R&D Blueprint—Scientific Advisory Group members. Available at: https://www.who.int/blueprint/about/sag-members/en/. Accessed March 21, 2020. 8. Simpson S, Kaufmann MC, Glozman V, et al. Disease X: accelerating the development of medical countermeasures for the next pandemic. Lancet Infect Dis. 2020;20(5):e108–e115. 9. Cousins S. WHO hedges its bets: the next global pandemic could be disease X. BMJ. 2018;361:k2015. 10. Cheng A, Van den Hurk A, Webb C, et al. 5 virus families that could cause the next pandemic, according to the experts. The Conversation. 2022. Available at: https://theconversation.com/5-virus-families-that-could-cause-the-next-pandemic-according-to-the-experts-189622. Accessed September 5, 2022. 11. Campbell D. Bacteria developing new ways to resist antibiotics, doctors warn. The Guardian. 2019. Available at: https://www.theguardian.com/society/2019/sep/11/bacteria-developing-new-ways-resist-antibiotics-doctors-warn. Accessed March 20, 2020. 12. Watson OJ, Barnsley G, Toor J, et al. Global impact of the first year of COVID-19 vaccination: a mathematical modelling study. Lancet Infect Dis. 2022;22:1293–1302. 13. Dimitrios G, Mario C, Stanley AP, et al. CEPI: driving progress towards epidemic preparedness and response. Epidemiol Rev. 2019;41(1):28–33.