How long symptoms appear after exposure and infection?
Similarities
Differences
For both COVID-19 and flu, 1 or more days can pass between a person becoming infected and when he or she starts to experience illness symptoms.
- If a person has COVID-19, it could take them longer to develop symptoms than if they had flu.
FLU
- Typically, a person develops symptoms anywhere from 1 to 4 days after infection.
COVID-19
- Typically, a person develops symptoms 5 days after being infected, but symptoms can appear as early as 2 days after infection or as late as 14 days after infection, and the time range can vary.
How long someone can spread the virus?
Similarities
Differences
For both COVID-19 and flu, it’s possible to spread the virus for at least 1 day before experiencing any symptoms.
- If a person has COVID-19, they may be contagious for a longer period of time than if they had flu
Flu
- Most people with flu are contagious for about 1 day before they show symptoms.
- Older children and adults with flu appear to be most contagious during the initial 3-4 days of their illness but many remain contagious for about 7 days.
- Infants and people with weakened immune systems can be contagious for even longer.
COVID-19
- How long someone can spread the virus that causes COVID-19 is still under investigation.
- It’s possible for people to spread the virus for about 2 days before experiencing signs or symptoms and remain contagious for at least 10 days after signs or symptoms first appeared. If someone is asymptomatic or their symptoms go away, it’s possible to remain contagious for at least 10 days after testing positive for COVID-19.
People at High-Risk for Severe Illness
Similarities
Differences
Both COVID-19 and flu illness can result in severe illness and complications. Those at highest risk include:
- Older adults
- People with certain underlying medical conditions
- Pregnant people
- The risk of complications for healthy children is higher for flu compared to COVID-19. However, infants and children with underlying medical conditions are at increased risk for both flu and COVID-19.
Flu
- Young children are at higher risk of severe illness from flu.
COVID-19
- School-aged children infected with COVID-19 are at higher risk. Developing rare but severe complication of COVID-19.
Complications
Similarities
Differences
Both COVID-19 and flu can result in complications, including:
- Pneumonia
- Respiratory failure
- Acute respiratory distress syndrome (i.e. fluid in lungs)
- Sepsis
- Cardiac injury (e.g. heart attacks and stroke)
- Multiple-organ failure (respiratory failure, kidney failure, shock)
- Worsening of chronic medical conditions (involving the lungs, heart, nervous system or diabetes)
- Inflammation of the heart, brain or muscle tissues
- Secondary bacterial infections
Flu
- Most people who get flu will recover in a few days to less than two weeks, but some people will develop complications.
COVID-19
- Additional complications associated with COVID-19 can include:
- Blood clots in the veins and arteries of the lungs, heart, legs or brain
