Question: What is the timing of the clinical course progression of COVID-19? How long between becoming infected, becoming sick, needing hospitalization, etc?

Answer: Like everything else COVID-related, we are still learning. Here’s a brief timeline based on what we currently know, which is limited (so this is likely to change as we learn more):

Average Time [all of these estimates are based on data from Wuhan, China]

• Infection to symptoms: 5 days (most symptoms appear between 4–7 days)
• Symptoms to doctor visit: generally 5–6 days
• Symptoms to hospitalization: 7 days, 9 days, 12.5 days (depends on data source/study population)
• Symptoms to ICU admission: 10 days (range: 6–12 days)

We know from data from Wuhan, China that the average time from infection to symptom onset is 5 days with the preponderance of symptoms occurring 4–7 days after infection. We also estimate — again, based on the first 425 confirmed cases in Wuhan — that time from illness onset to first doctor visit is about 5 days, and the average duration of illness onset to hospitalization rages generally from 9 to 13 days. Other data presented back in February from one hospital in Wuhan showed that the average time from symptom onset to hospitalization is 7 days (range: 4–8 days) and average time from symptom onset to ICU admission is 10 days (range: 6–12 days). A recent paper published in Lancet tracking the clinical progression of the first five patients diagnosed in Europe gives this nice visualization, which highlights how different the clinical course is by individual — each of these patients had very different background characteristics and outcomes.

Question: Will a history of running help reduce COVID-19 severity? Like, if I have enhanced lung capacity from exercise, will that help?

Answer: Exercise is good for you, so keep at it! When it comes to answering your question, we don’t have this type of data for COVID-19 specifically (no surprise there), but we can look at the relationship between exercise and respiratory disease mortality since it’s been studied in other contexts.

• First, there’s a pretty big body of evidence to support the positive relationship between exercise and immune function.
• Second, there’s been some scientific debate about the short-term effects of high-intensity exercise on the immune system. A review of the evidence published in 2018 shows that we do not need to worry — “rather than suppressing immunity, contemporary evidence shows that an acute bout of exercise improves immune surveillance.”
• Third, when we look more specifically at the relationship between exercise and another respiratory condition — pneumonia — we find some marginal benefit: a) “The risk of community-acquired pneumonia decreased with increasing physical activity among women” but that was not the case among men in the study; b) “Women in the highest quintile of walking were less likely to develop pneumonia compared to women who walked the least (multivariate adjusted RR=0.82; 95% CI, 0.69–0.98)” but there was no statistically significant difference among the other categories (this study only included women); c) “Higher doses of running and walking were associated with lower risk of respiratory disease, pneumonia, and aspiration pneumonia mortality in a dose-dependent manner, and the effects of running and walking appear equivalent.”