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2020-

2020-11-19 c
THE COVID-CON III
"Absence of (scientific) evidence is not, of course, evidence of absence, and there is plenty of anecdotal evidence of the harm wearing masks does"

Danish Mask Study: Masks Do Not Protect From Coronavirus

The suppressed Danish mask study – the largest randomised controlled trial to date that had been rejected by three top journals, apparently on political grounds (read the interview with the authors here) – was finally published yesterday.

The headline result is that in the study masks do little or nothing to lower the infection rate. It found a 2.1% vs 1.8% infection rate for unmasked vs masked groups (with around 3,000 participants in each group initially). However, due to low virus prevalence these figures correspond to only 53 and 42 participants respectively so the authors had to state that the result is not statistically significant (too few infections to be confident it’s not random).

The most striking finding is that when you look at participants who report wearing face masks “exactly as instructed” as opposed to just “predominantly as instructed” the proportion infected rises from 1.8% to 2.0% (22 participants). This is the wrong way round – if masks are helping, using them better should reduce infections – and 2.0% is almost identical to the 2.1% infected without masks. This suggests the lower figure for all mask wearers was probably just noise.

A few more observations:

•Reported symptoms did not differ between those who wore masks and those who didn’t, giving no support to the masker theory that masks make the disease milder (or provide immunity) by reducing viral load.

•For other respiratory viruses the study found 0.5% vs 0.6% infection rate (9 vs 11 participants) for masks vs non-masks, so again almost the same, supporting the primary finding.

•Although 91 participants reported someone else in their household contracting COVID-19 during the study (52 masked and 39 non-masked), only three reported then catching it themselves – two with masks and one without. Strange, because the home is usually found to be a primary source of transmission.

•The study looks at protecting the wearer not others (i.e., source control, the usual justification for masks). It couldn’t look at source control as the study took place in April and May before masks were mandated or in widespread use.

With insufficient infections to achieve statistical significance, despite involving over 6,000 participants, the study leaves a need for further studies that are large enough and in areas of high enough prevalence to achieve statistical significance.

We can’t draw firm conclusions about precise differences in infection rates from this study. However, we can say that wearing a surgical mask even “exactly as instructed” does not appear to prevent infection completely – does not appear to prevent it much at all. And if that’s the case for surgical masks, how much more for cloth masks? (read more)

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