Not everyone who becomes seriously ill fits the high-risk profile. In every infectious disease outbreak, there are unexplained cases that defy the statistics, such as severe illness striking a young, healthy person who would have been expected to become just mildly sick. The physician in China who was penalized for alerting colleagues to the outbreak there, Dr. Li Wenliang, died from the disease at age 34.
Which virus makes you sicker?
In the current season, there have been at least 34 million cases of flu in the United States, 350,000 hospitalizations and 20,000 flu deaths, according to the C.D.C. Hospitalization rates among children and young adults this year have been unusually high.
There would be even more illnesses and deaths if there were no flu vaccine. Most people recover in less than two weeks, and sometimes in just days.
By contrast, at least 90,000 people in the United States have been infected with the new coronavirus by late March, and there have been at least 1,400 deaths. There are no treatments or vaccines for the coronavirus, only supportive care for infected people.
Most cases of coronavirus infection are not severe, but some people do become quite sick. Data from the largest study of patients to date, conducted in China, suggests that of coronavirus patients receiving medical attention, 80 percent had mild infections, about 15 percent had severe illnesses, and 5 percent were critical. (But many of the mild infections included patients with pneumonia, experts later learned.)
The first symptoms, fever and cough, are similar to that of the flu, so the diseases can be hard to tell apart without a test to identify the virus. Pneumonia is common among coronavirus patients, even among those whose cases are not severe.
Experts think there may also be many people with no symptoms at all, or such mild ones that they never bother to seek medical attention. Because those cases have not been counted, it’s not possible now to know the real proportion of mild versus severe cases.