Symptoms. Some
symptoms of flu and Covid-19 are similar: a dry cough and fever. Covid-19 more often causes shortness of breath and difficulty breathing -- a sign to seek immediate medical attention. Influenza causes aches, fatigue, headache and chills; these appear to be less common with Covid-19. Flu symptoms tend to come on abruptly, getting worse in a day or two. With Covid-19, symptoms may be more gradual and take several days to get worse. If you are sneezing, or have a stuffy or runny nose, the good news is that you probably just have a garden-variety common cold -- ironically, one possibly caused by a different coronavirus.
Covid-19 is more infectious than flu. It appears a person who is infected with Covid-19 spreads it to more people than the flu, so it may spread farther and faster than flu.
Covid-19 is more likely to kill than flu. On average, about 1 in 1,000 people who get flu die from it -- mostly the elderly and people with underlying health conditions, but flu sometimes kills healthy young people and pregnant women. We don't know the precise case fatality ratio for Covid-19 because of incomplete testing of possible cases and insufficient information about outbreaks. But so far, Covid-19 appears much deadlier than seasonal flu, and quite possibly
deadlier than the flu pandemics of 1957 and 1968, each of which killed more than 1 million people around the world. Those pandemics had estimated case fatality ratios far below 1% -- and Covid-19 may kill more than 1 in 100 people who get sick with it. This is not as high as the
1918 flu pandemic, which has been estimated to have killed 2.5 of 100 who it made sick, killing an estimated 675,000 Americans at a time when our population was one-third what it is today. As with the flu, older people and those with serious health conditions such as heart or lung disease, cancer or diabetes are at much higher risk.
And there is a fundamental difference in how flu and Covid-19 kill. Many deaths from flu are caused by
secondary bacterial pneumonia and heart attacks that develop after the flu has weakened someone's resistance. With Covid-19, most deaths are caused by
acute respiratory distress syndrome (ARDS), which causes already-damaged lungs to fill with fluid, and makes breathing difficult. Unlike pneumonia, there is no pharmaceutical treatment for ARDS. That is why a potential
shortage of ventilators is so dangerous: They are the last-ditch supportive treatment for Covid-19 while the body heals itself.
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