Too Good to be True?
Inactivation times for Covid-19 in sunlight could be less than 5 minutes ..
Welcome to an earlier posting this week …. (and maybe at this time in future weeks)
What a coincidence! In my last two postings here I showed theoretical calculations of inactivation times in sunlight for viruses like Covid-19. The times I estimated were about an hour in summer sunlight, rather longer than for other micro-organisms we’d considered previously. At a White House Press Briefing on April 23rd, a report emerged of a direct experiment attributed to the Department of Homeland Security that implied even more rapid inactivation of Covid-19 by summer sunlight.
But press releases aren’t the most reliable source of scientific information, particularly if Donald Trump is involved. Some healthy skepticism is called for.
So, while the results look promising, I await confirmation in the peer-reviewed literature to see exactly what was done. For example, did they use real summer sunlight? If so, where and when? Or was it just simulated sunlight from an artificial solar simulator in a laboratory, which may contain more short-wavelength (i.e., more damaging) UV than in real sunlight.
The slide used in the briefing is shown above. Their reported half-life of 2 minutes in “summer” corresponds to a 90 percent inactivation time of about 7 minutes.
If the results of this (hazardous) experiment do turn out to be true, then one or both of these must be true:
The inactivation dose for Covid-19 must be much less than for other viral strains tested (probably ~1 Jm-2, which is comparable with that for the most sensitive micro-organism we considered previously), and/or
The action spectrum for damage must be less steep than the (published) action spectra I assumed.
I’ll keep you posted if the study ever sees the light of day in the peer-reviewed literature .
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