What I would like everyone to take away from this whole asymptomatic/pre-symptomatic debate:
- There is evidence that people can transmit to others before they develop symptoms (pre-symptomatic period).
- This means that people without current symptoms can be infectious. 1/8
- This is observed by tracing data. There are instances where someone was infected but their only possible exposure was a pre-symptomatic contact.
- To be sure, we must rule out all other potential sources of infection (fomites, untraced contacts). 2/8
- Outside of these instances that show it can occur, it is difficult to measure how often it occurs.
- We can look at likely pairs of cases (infected family members) and see who had symptom onset first, and measure how far apart these onsets were. 3/8
- Given what we know about how long it takes from infection to developing symptoms, we can estimate whether transmission was likely before or after the first person developed symptoms. We average across a lot of people.
- For this, we need high quality contact tracing data. 4/8
- Another source of evidence is that people have high viral load around the time when they develop symptoms.
- But knowing someone has high viral load is not the same as knowing they can infect others. 5/8
- Some people never develop symptoms (fully asymptomatic).
- We don't know how often they transmit to others, mostly because they are so difficult to find, and even more difficult to link in chains of transmission. Imagine all of the above challenges, but even harder. 6/8
- As a result, direct evidence of how frequently asymptomatic people transmit is even more limited.
- Again, we need better contact tracing data and more testing to sort this out. 7/8
- This is a new virus. There is still a lot of uncertainty.
- It is hard to communicate this level of uncertainty to the general public.
- But we know that people without symptoms can transmit, and so our policies and actions must reflect this. 8/END
(H/t @SunKaiyuan for being my go-to expert on this topic.)
You can follow @nataliexdean.
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