Current state of COVID knowledge
November 29, 2020
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Dr John Campbell Episodes Around November 29, 2020
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28:19Now PlayingCurrent state of COVID knowledge
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as posted by the channelCurrent state of knowledge, 29th November
US hospitalisations
Infection
Human infectious dose, SARS-CoV-2, unknown by all exposure routes
However
Based on human exposure to other coronaviruses
and animals exposure
the dose at which 50% of humans become infected is 10 to 1,000 plaque-forming units (PFU)
UK, human exposure trials in January 2021 to identify the infectious dose of SARS-CoV-2
Golden Syrian hamsters
Exposure to 56,000 PFU via the intranasal route developed clinical symptoms
Immunosuppressed, severe clinical symptoms (including death) after exposure to 100-10,000 PFU
We need to know
Human infectious dose;
by aerosol
surface contact (fomite)
fecal-oral routes
other potential routes of exposure
Most appropriate animal model(s) to estimate the human infectious dose for SARS-CoV-2
Does exposure dose determine disease severity?
Transmission
Exhaled breath may emit 105-107 genome copies per person per hour
100, 000 to 10,000,000
Droplets
Aerosols
Fomites
Close = a combined total of 15 minutes within 6 feet of an infected person in a 24-hour period
Infectious for 1-3 days prior to symptom onset, 40%
Asymptomatics, 12%
Five days after symptom onset
Asymptomatic individuals can transmit disease as soon as 2 days after infection
Asymptomatic children may have substantially lower levels of virus in their upper respiratory tracts than symptomatic children
In the US, symptomatic index cases resulted in transmission to approximately 53% of household members
SARS-CoV-2 may be spread by conversation and exhalation
Most transmission indoors, offices, restaurants, bars, gyms
Clusters are often associated with large indoor gatherings
Undetected cases play a major role in transmission
Most cases are not reported
Individuals who have clinically recovered but test positive for COVID-19 are unlikely to be infectious
We need to know
Relative contribution of different routes of transmission (e.g., fomites, aerosols, droplets)
How common is transmission from bodily fluids like semen, urine, and feces?
How infectious are young children compared to adults?
What is the emission rate of infectious SARS-CoV-2 particles while breathing, talking, coughing, singing, or exercising
taking into account variation in viral load in the upper and lower respiratory tract?
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