Clinical Public Health, U.S. Centers for Disease Control and Prevention, World Health Organization, Nature, bioRxiv, China, United States
development

Organisations. U.S. Centers for Disease Control and Prevention CDC, World Health Organization WHO, Nature, bioRxiv
Period. 21 - 28 May 2020

A study in Physics of Fluids reporting on the mechanisms of coughing and airborne transmission of viruses. While cough droplets in typical environmental conditions will travel less than the widely mandated 2 meters for social distancing, the authors note that changes in air flow and other environmental properties (e.g. wind, temperature, humidity) can cause that figure to rise quite dramatically. For example, even modest winds (i.e. 4 to 15km/h) could result in saliva droplets dispersing and traveling up to 6 meters. Although the study provides guidelines on the mechanical aspects of droplet transmission, experts suggest the computer simulation may not capture the process of dilution, while the relationship to viral transmission also remains unclear.

A non-peer reviewed pre-print of a study on bioRxiv examining mutations of the novel Coronavirus did not find any variants that had increased transmissibility. While this suggests none of the known mutations are cause for immediate concern, the findings do not rule out the possibility of emerging future variants with different properties. The Director of the Francis Crick Institute has also suggested testing the study conclusions in functional assays of frequently occurring variants in order to examine their proposed mechanisms.

The U.S. Centers for Disease Control and Prevention issued a new guidance with five COVID-19 planning scenarios to public health authorities based on lower and upper bounds across three parameters: virus transmissibility and disease severity, transmission prior to onset of symptoms, and infections that don’t develop symptoms. One of the scenarios, representing the CDC’s “current best estimate about viral transmission and disease severity in the U.S.” (assuming a R0 of 2.5), approximates 35% of COVID-19 infections may be asymptomatic, and that 0.4% of symptomatic positive cases result in mortality. Epidemiologists, however, question the estimates of symptomatic case fatality rate in the scenarios – from 0.2% (least severe) to 1% (most severe) – which is lower than the reported range in the literature.

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