New APPS

It’s fairly clear that one of the keys to living with Covid-19 is understanding the dynamics of transmission: absent something more nuanced than what we have, “stay 6 feet away from everyone at all times!” becomes the only public health advice that can be given.  Getting past the initial maximin strategy requires better data on everything.  There’s an interesting Twitter thread by Dr. Muge Cevik (St. Andrews) that collates some of the recent studies about transmission within and through social groups.

A lot of discussion recently about transmission dynamics, most of which are extrapolated from viral loads & estimates. What does contact tracing/community testing data tell us about actual probability of #COVID19 transmission(infection rate), high risk environments/age?
[thread]

— Dr Muge Cevik (@mugecevik) May 4, 2020

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It’s not a formal meta-analysis or anything like that but there’s emerging confirmation for the idea that most transmission depends on sustained, close contact, and that children do not appear to be a primary vector for the disease (this latter one is enormously important, because nobody knows for sure what should be done about schools).  She summarizes at the end (the paragraph breaks are mine):

“While the infectious inoculum required for infection is unknown, these studies indicate that close & prolonged contact is required for #COVID19 transmission. The risk is highest in enclosed environments; household, long-term care facilities and public transport. High infection rates seen in household, friend & family gatherings, transport suggest that closed contacts in congregation is likely the key driver of productive transmission. Casual, short interactions are not the main driver of the epidemic though keep social distancing! Increased rates of infection seen in enclosed & connected environments is in keeping with high infection rates seen in megacities, deprived areas, shelters. A recent preprint demonstrates that #COVID19 epidemic intensity is strongly shaped by crowding.

“Although limited, these studies so far indicate that susceptibility to infection increases with age (highest >60y) and growing evidence suggests children are less susceptible, are infrequently responsible for household transmission, are not the main drivers of this epidemic.”

“Finally, these studies indicate that most transmission is caused by close contact with a symptomatic case, highest risk within first 5d of symptoms. To note: this preprint suggests that most infections are not asymptomatic during infection.  In conclusion, contact tracing data is crucial to understand real transmission dynamics. Cautionary note: This data & interpretation is based on the available evidence as of May 4th. Our understanding might change based on community testing/lifting lockdown measures.”