1.4 THE PANDEMIC THREAT
A pandemic is a global disease outbreak. An influenza pandemic occurs when a new
influenza A virus emerges for which there is little or no immunity in the human population, begins to cause serious illness and then spreads easily person-to-person worldwide. Three such pandemics have occurred in the last century; in 1918, 1957, and 1968 each causing millions of deaths. Each of these pandemics was preceded by development of a new virus through re-assortment of the human and animal influenza virus genes.
1918: Spanish Flu
The Spanish Influenza (H1N1) pandemic is the catastrophe against which all modern
pandemics are measured. It is estimated that approximately 20 to 40 percent of the
worldwide population became ill and that over 40 million people died. One of the most
unusual aspects of the Spanish flu was its ability to kill young adults. The reasons for this remain uncertain. With the Spanish flu, mortality rates were high among healthy adults as well as the usual high-risk groups. The attack rate and mortality was highest among adults 20 to 50 years old. The severity of that virus has not been seen again.
1957: Asian Flu
In February 1957, the Asian influenza (H2N2) pandemic was first identified in the Far East. Immunity to this strain was rare in people less than 65 years of age, and a pandemic was predicted. In preparation, vaccine production began in late May 1957, and health officials increased surveillance for influenza outbreaks.
Unlike the virus that caused the 1918 pandemic, the 1957 pandemic virus was quickly
identified, due to advances in scientific technology. Vaccine was available in limited supply by August 1957. Although the Asian influenza pandemic was not as devastating as the Spanish one, there were at least 70,000 U.S. deaths and 1-2 million deaths worldwide.
1968: Hong Kong Flu
In early 1968, the Hong Kong influenza (H3N2) pandemic was first detected in Hong Kong. The number of death for this pandemic was 34,000 in the U.S. and 700,000 deaths worldwide which was less than half of the deaths in USA during the Asian flu pandemic, making it the mildest pandemic in the 20th century. There could be several reasons why fewer people died due to this virus. First, the Hong Kong flu virus was similar in some ways to the Asian flu virus that circulated between 1957 and 1968. Earlier infections by the Asian flu virus might have provided some immunity against
the Hong Kong flu virus that may have helped to reduce the severity of illness during the Hong Kong pandemic. Also, improved medical care and antibiotics that are more effective for secondary bacterial infections were available for those who became ill thus reducing the fatality.