In an average year, approximately what percent of Americans contract influenza?

In an average year, approximately what percent of Americans contract influenza?

• A. About 20 percent
• B. About 5 percent
• C. About 50 percent
• D. About 1 percent

Answer: (A)

Influenza infections during a typical season affect a sizable portion of the population. The main idea is that a large fraction of people become infected, but many cases go unreported because symptoms resemble a cold and not everyone seeks testing. Because of this, surveillance estimates place the average annual infection rate around 20% of Americans. The figure can vary by season, with some years higher or lower, but about one in five is a reasonable general expectation. The other options are outside what is typically observed: 1% is too low to account for the usual burden, 5% is possible in milder years but not the average, and 50% would imply half the population is infected, which is not supported by consensus data.

Influenza infections during a typical season affect a sizable portion of the population. The main idea is that a large fraction of people become infected, but many cases go unreported because symptoms resemble a cold and not everyone seeks testing. Because of this, surveillance estimates place the average annual infection rate around 20% of Americans. The figure can vary by season, with some years higher or lower, but about one in five is a reasonable general expectation. The other options are outside what is typically observed: 1% is too low to account for the usual burden, 5% is possible in milder years but not the average, and 50% would imply half the population is infected, which is not supported by consensus data.