2/ We review environmental viability of virus in experimental and real world settings.
RNA reported in many real world studies, but at very low copy counts
Viable virus assessed for only rarely and in those instances only isolated occasionally, also at very low levels
3/ We review viral and host factors that impact transmission
Children under ten appear half as susceptible but relative probability of transmission from children compared with adults not well understood
Virus with D614G mutation is associated with higher in vivo viral loads
4/ Respiratory transmission dominant
Droplet vs aerosol model = oversimplification
That proximity is key determinant of transmission suggests relative importance of classical droplet mode, but in indoor environments w/ poor ventilation, can transmit at a distance thru aerosols
5/ Despite concerns about fomite transmission, there is no conclusive evidence to support this mode of transmission and if it happens at all is likely only responsible for a minority of spread
That said good hand hygiene is protective against acquisition of virus
6/ Some domestic pets can be infected but no documented transmission from domestic pets to humans. However, minks can be infected and there is documented transmission from minks to humans
7/ It was unclear for a while, but there is now conclusive evidence for rare vertical transmission
8/ There is no conclusive evidence for fecal-oral spread. There is currently one cluster report potentially caused by fecal-aerosol spread, though this is likely extremely unusual
There is no current evidence for sexual or bloodborne transmission of the virus
9/ The "period of infectiousness" is best known for immunocompetent adults who develop symptoms
Infectiousness peaks just before or right around symptom onset and declines quickly after, despite ongoing RNA shedding
10/ In patients with mild or moderate disease, infectious virus cannot be cultured after around 8 days of symptom onset.
In those with severe or critical disease infectious virus can be cultured a bit longer, with the latest isolation of infectious virus 20 days after symptoms
11/ Despite isolation of infectious virus, there are no documented late transmissions, after about a week of symptoms
12/ Heterogeneous transmission is the explanation for superspreading events, which are an important feature propagating the pandemic
The figure models heterogenous transmission. An index case transmits to 2 secondary cases; 1 has no other transmissions while other transmits to 4
13/ Outside of superspreading events the household is a key site for transmission. After superspreading events further transmission frequently occurs in households
14/ Conclusions
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3/ Second CORIMUNO-TOCI also found no benefit, but there was some drama with this study when DSMB members quit after a press release they disagreed with in the late spring 2020
2/ They report their mAb cocktail had 100% efficacy in preventing symptomatic COVID-19 (8/223 placebo vs. 0/186 REGEN-COV)
They also report lower ASYMPTOMATIC infection (15/223 placebo vs. 10/186 REGEN-COV)
3/ Among the infections, way less peak viral load and viral shedding seen
- Avg peak VL >100x placebo vs REGEN-CoV
- Infections in REGEN-CoV lasted <1 week, while 40% in placebo lasted 3-4 weeks
(would be nice to see VL comparison just for asymptomatic cohorts)
2/ An early transmission report of suggested transmission is possible prior to symptom onset.
Need to distinguish between: persistently asymptomatic infection (no symptoms attributable to the virus for the duration of infection) and presymptomatic state
2/ Wide range of asymptomatic proportion reported in the literature from 4% to >80%. Systematic reviews provide best estimates and suggest values closer to 20% medrxiv.org/content/10.110…
3/ Our understanding of the symptom spectrum of SARS-CoV-2 infection has evolved over the last 9 months, with anosmia and GI symptoms often not included in early reports. By not including these mild or atypical symptoms, the estimated asymptomatic fraction may be overestimated