Question: Is there information about the average duration of the illness?  I’m especially curious about illness duration for mild cases who don’t need hospitalization.

Answer: We’ve talked about this a bit in the past (most recently Q&A of 10/5), but it’s worth revisiting, especially since I don’t think I’ve synthesized this information previously.  So here goes (see also Table 1 and Figure 1):

• Most people will experience mild symptoms or moderate illness.* 
  • WHO estimates that 85-90 percent of cases are mild to moderate.
  • CDC’s current best estimate is that 40 percent of all cases are asymptomatic.
• A substantial proportion of cases will be severe.
  • WHO estimates that 10-15 percent of cases will become severe; 5 percent become critically ill.
• Recovery varies based on disease severity and individual characteristics.
  • Asymptomatic people are considered non-contagious and are counted as recovered 10 days after their first positive test.   
  • People with mild/moderate symptoms generally recover in 2 weeks. (WHO)
  • People with severe symptoms generally recover in 6 weeks, though it can be longer. (WHO)
  • Among symptomatic mild/moderate cases, a substantial proportion (1 in 3) report not returning to full health within 2-3 weeks of symptom onset. (CDC)
  • The proportion of “long-haulers” is still unknown, but the numbers are growing (for more, see Q&A of 10/5 or these articles published in JAMA and Nature.

*For a definition of mild/moderate/severe, see NIH treatment guidelines. 

Table 1. Disease Severity and Illness Duration

Figure 1. Timeline of illness duration (from WHO)