‘Moderate humidity likely to deter virus’

A 2018 study in the peer-reviewed Applied and Environment Microbiology concluded that influenza and coronaviruses thrived when the relative humidity (RH) exceeded 85% or dipped below 60%. RH is the proportion of water vapour in the air compared to what’s the maximum possible. There is a “significant decrease in infectivity at mid-range RHs (60 to 85%),” the paper notes.

It is important to note that these studies didn’t study actual coronaviruses but a bacteriophage Phi6, which is considered a safer surrogate.

A similar experiment reported in the same journal in 2010, that tested the ability of viruses to survive on stainless steel surfaces, found that at 4°C, infectious viruses persisted for as long as 28 days, and the lowest level of inactivation occurred at 20% RH.

Inactivation was quicker at 20°C than at 4°C at all humidity levels; the viruses persisted for 5 to 28 days, and the “slowest inactivation” occurred at low levels of RH.

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