Oswin et al.: "Under all conditions measured, the majority of SARS-CoV-2 virus is inactivated in 10 min of aerosolization." Dynamics of SARS-CoV-2 infectivity with changes in aerosol microenvironment

by Paul Alexander

...'at 90% RH (relative humidity), droplet remains homogenous & aqueous, & the viral stability is sustained for the first 2 min, beyond which it decays to only 10% remaining infectious after 10 min.'

I leave it up to you to ponder the implications of all we were put through for 2.5 years and still today in response to this.

“The initial rate of infectivity loss was found to correlate with physical transformation of the equilibrating droplet; salts within the droplets crystallize at relative humidities (RHs) below 50%, leading to a near-instant loss of infectivity in 50 to 60% of the virus. However, at 90% RH, the droplet remains homogenous and aqueous, and the viral stability is sustained for the first 2 min, beyond which it decays to only 10% remaining infectious after 10 min. The loss of infectivity at high RH is consistent with an elevation in the pH of the droplets, caused by volatilization of CO2 from bicarbonate buffer within the droplet. Four different variants of SARS-CoV-2 were compared and found to have a similar degree of airborne stability at both high and low RH.”

The role of efflorescence in SARS-CoV-2 airborne loss of infectivity. (A) Comparison of the infectivity from Fig. 1B after 2-min levitations at constant 40% RH (purple bar) and 70% RH (green bar) with levitations where the RH has been cycled between 75 and 40% RH in one levitation (blue bar labelled cycled RH). The bars show the average % infectivity with error bars showing the standard error; the white circles show the % infectivity from the individual measurements. (B) CK-EDB measurements showing the phase behavior of levitated MEM droplets as the RH is cycled between 75 and 40%. RH is initially set at 75%, lowered to 40% at 14 s, raised to 75% at 24 s, lowered to 40% at 32 s, and finally raised to 75% at 41 s. Structural information about the droplet is denoted by the color of the data points as per Fig. 2A. (C) Images showing the changes in particle morphology that take place while MEM 2% FBS is airborne. The Top images are from the falling droplet column and showing the initial droplet generated by the dispenser on the Left, the droplet after 1.6 s of evaporation at 28% RH in the Center, and three different particles after they have undergone phase change on the Right. The Bottom shows two SEM images of droplets effloresced at 28% RH (Left) and 40% RH (Right). The scale bar is 5 µm long. (D) Percent Infectivity of SARS-CoV-2 (REMRQ0001) measured after levitation for 5 min at three different temperatures and RHs. Bars show the mean of five measurements with error bars showing the standard error.