How likely is a flu pandemic?
Most scientists believe that occasional influenza pandemics are inevitable, like earthquakes or hurricanes. Influenza pandemics have been documented several times in the 20th century and earlier, including 1918-19 (the most severe on record, with an estimated 50 million deaths worldwide), 1957 and 1968. Unfortunately, scientists cannot predict exactly when a new influenza pandemic will occur, which influenza strain will be responsible, or how severe the pandemic will be. This means that public health authorities, like the people who track earthquakes or hurricanes, must be on alert to try to spot pandemics as early as possible. There are many possible influenza strains that are novel to the human population, especially in wild waterfowl, and influenza viruses are constantly evolving. Luckily, many of these influenza strains are not able to infect humans, and efficient person-to-person spread is difficult for novel influenza viruses to achieve. For this reason, pandemics generally occur
