A new lethal infectious disease outbreak is inevitable, experts say. But global health leaders struggle to reach consensus on vaccine and antiviral drug development, information sharing, and primary prevention tactics. And the United States, which has historically been a major financial contributor to international public health efforts, pulls away from cooperation as President Donald Trump threatens to stop sending foreign aid.
In the summer of 1968, a strain of influenza known as H3N2 emerges in Hong Kong, then a British colony, and travels rapidly across East Asia and into Australia and Europe. Within a year, it had reached the United States and South America. This pandemic killed an estimated one million people, mostly from the over-65 crowd. Descendants of the virus still circulate seasonally today.
An epidemic is a community-level outbreak of a disease that exceeds expectations for the area based on past infection rates, such as those reported in health department surveillance or disease registries. However, an increased number of cases does not always indicate an epidemic; factors like variations in reporting procedures, sudden changes in population size, and weather can all affect the expected number of cases.
Some outbreaks are common-source, such as an outbreak of hepatitis A caused by eating at a restaurant that served raw chicken. In other cases, an outbreak is propagated, such as the spread of the novel flu strain H1N1 in 2009, which disproportionately affected younger people and those without previous exposure to influenza viruses.
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