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Delta vs original COVID
This appears to be a good study out of China.  They had an outbreak of Delta, involving 167 other cases from May 21 to June 18 (none after that date), where they had the index case and did case tracing of that initial case and then quarantined all close contacts of each subsequent cases.  For those in quarantine, they did daily PCR tests.

Excluding cases spread amongst family (where date of exposure would be hard to pin down), they calculated the time from exposure to first positive PCR test.  The average was 4.0 day, 2 days less than measured for the original COVID.  (Unfortunately, I don't see that they recorded symptom onset.).  

Their PCR tests were of samples taken from the nose (oropharyngeal swab).  On the first day of detection, the viral load was about 1200x the viral load measured from the original infection.

A problem I have with this is that I'd expect there to be variability of more than 24 hours since exposure for tests once a day.  Was it 73 hours or 119 hours since exposure?  A measurement at 73 hours may have barely enough virus to detect, while at 119 hours, maybe the body is already fighting the infection.   I haven't looked in detail at the study to see if they address my concern.

The initial high viral load in the nose followed by decreasing levels is consistent with high viral loads at initial detection for the original COVID.

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