The World Health Organization warned that another global pandemic is inevitable and may be caused by a theoretical pathogen called “Disease X.”

This warning underscores a critical vulnerability in global health infrastructure. Experts said that current systems remain poorly prepared to handle a new outbreak, which could lead to widespread mortality if response gaps are not closed.

Director-General Tedros Adhanom Ghebreyesus said, "The next pandemic is a matter of when, not if it will occur."

Health experts have identified four specific viruses that could potentially evolve into “Disease X” [1]. These pathogens pose a significant risk of triggering a large-scale health crisis. The risk is compounded by climate change, which experts said expands the natural habitats of viruses and increases the likelihood of zoonotic spillover.

To address these risks, the United Nations established the International Day of Epidemic Preparedness, which was first celebrated on Dec. 27, 2020 [2]. The initiative aims to keep the lessons of the COVID-19 pandemic at the forefront of policy discussions.

International efforts to coordinate a response have progressed with the adoption of the WHO Pandemic Accord in 2025 [3]. This agreement is intended to standardize how nations share data, and resources during a crisis. However, experts said that the lessons from COVID-19 continue to expose critical gaps in national health systems that the accord must address.

Global health officials continue to urge nations to invest in surveillance and vaccine infrastructure to prevent a repeat of previous systemic failures.

“"The next pandemic is a matter of when, not if it will occur."”

The focus on 'Disease X' represents a shift from reactive to proactive epidemiology. By preparing for a hypothetical pathogen rather than a known one, the WHO is attempting to build a flexible global defense system. The effectiveness of this strategy depends on whether the 2025 Pandemic Accord can translate into actual funding and infrastructure in low-income regions, where the next spillover is most likely to occur.