Disease X stands as a symbol for a subset of emerging infectious diseases rising to prominence as a significant challenge to global health security. A comprehensive review by Fei and Huang (2024) delves into the historical context, precise definition, and illustrative case studies of disease X, including notable examples, such as COVID-19, SARS, and Ebola. The experts also examine the potential origins of disease X, with a particular focus on zoonotic pathways and the influence of environmental factors. They also present proposed strategies aimed at the prevention and containment of disease X, emphasizing the critical role of vigilant surveillance, swift response mechanisms, and the necessity of fostering international cooperation.

The authors point to the COVID-19 pandemic as an example of what could have been construed as disease X: "The COVID-19 pandemic, caused by the novel coronavirus SARS-CoV-2, has emerged as one of the most significant global health crises in recent history. The unprecedented scale and impact of the COVID-19 pandemic have exposed the vulnerabilities of global health systems and underscored the need for robust preparedness and response mechanisms [16,17]. The rapid spread of the virus, facilitated by international travel, urbanization, and population density, has emphasized the interconnectedness of modern society and infectious disease dynamics."

They continue, "COVID-19 has presented a myriad of challenges for public health authorities, healthcare systems, and governments worldwide. The virus has exhibited a wide spectrum of clinical manifestations, ranging from mild respiratory symptoms-to-severe pneumonia, acute respiratory distress syndrome (ARDS), and multi-organ failure. Vulnerable populations, including the elderly and those with underlying health conditions, have been disproportionately affected by the virus. Efforts to control the spread of COVID-19 have included widespread testing, contact tracing, quarantine measures, and social distancing guidelines. However, containment efforts have been hampered by factors, such as asymptomatic transmission, limited testing capacity, and vaccine hesitancy. The development and distribution of vaccines against COVID-19 have represented a significant milestone in the pandemic response, offering hope for controlling transmission and mitigating the impact of the virus. Despite vaccination efforts, the emergence of new variants of COVID-19 has raised concerns about vaccine effectiveness and the potential for future waves of infection. Additionally, disparities in vaccine distribution and access have underscored the need for global solidarity and collaboration in addressing the pandemic."

They add, "As the COVID-19 pandemic continues to evolve, ongoing research efforts are focused on understanding the viral transmission dynamics, immune response, and long-term health effects. Lessons learned from the pandemic will inform future preparedness and response efforts, emphasizing the importance of investing in resilient healthcare systems, pandemic preparedness, and international cooperation."

Reference: Fei Y and Huang J. Unveiling Disease X: Strategies for Tackling the New Frontier of Infectious Diseases. Zoonoses. May 28, 2024