Pandemic Preparedness and Response — Lessons from the H1N1 Influenza of 2009

A number of viruses have pandemic potential.For example, the coronavirus responsible for the severe acute respiratory syndrome (SARS), which first appeared in southern China in November 2002, caused 8096 cases and 774 deaths in 26 countries before coming to a halt by July 2003 mainly owing to isolation and quarantine. 1 In terms of persistence, versatility, potential severity, and speed of spread, however, few viruses rival influenza virus.Endemic in a number of species, including humans, birds, and pigs, influenza virus causes annual outbreaks punctuated by occasional worldwide pandemics, which are characterized by sustained community spread in multiple regions of the world.Beyond spread, the degree to which a pandemic is defined according to the severity of the disease, or whether it may be simply described as often producing many illnesses and deaths, remains ambiguous.2 At its worst, pandemic influenza can be catastrophic: the great influenza pandemic of 1918-1919 is estimated to have infected 500 million persons worldwide and to have killed 50 to 100 million persons. 3 In a typical year of seasonal outbreaks in the Northern and Southern Hemispheres, influenza virus causes as many as 5 million cases of severe illness in humans and 500,000 deaths.4 Over the past decade, sporadic cases of severe influenza and deaths in humans have been caused by a number of avian influenza A viruses, including the H5N1 virus, first detected in 1997, and the H7N9 and H10N8 viruses, first reported in 2013.Such sporadic cases may be harbingers of a gathering pandemic, but the likelihood is difficult to judge because it is not known how frequently similar zoonotic episodes occurred silently in the past, when surveillance was more limited, and did not cause pandemics.The most recent global pandemic was caused by the influenza A (H1N1) strain, which was first detected in North America in 2009 (influenza A[H1N1]pdm09).This event prompted the first activation of provisions under the 2005 International Health Regulations (IHR), which went into effect in 2007.5 Deliberations that led to the 2005 IHR revisions were shaped by experience in the SARS outbreak of 2003.The regulations delineate the responsibilities of individual countries and the leadership role of the World Health Organization (WHO) in declaring and managing a public health emergency of international concern.The 2009 H1N1 pandemic presented a public health emergency of uncertain scope, duration, and effect.The experience exposed strengths of the newly implemented IHR as well as a number of deficiencies and defects, including vulnerabilities in global, national, and local public health capacities; limitations of scientific knowledge; difficulties in decision making under conditions of uncertainty; complexities in international cooperation; and challenges in communication among experts, policymakers, and the public.