Let’s look at the seven studies he uses to support his thesis (apparently the format doesn't produce numbers, so each bullet point is a number):
- 32 subjects, 16 wore masks, 16 did not. There was only one cold in each group. Obviously the small sample size, and particularly the fact that most controls did not get a cold, makes this study meaningless, and the authors themselves basically concluded this.
- The authors state, “There is some evidence to support the wearing of masks or respirators during illness to protect others, and public health emphasis on mask wearing during illness may help to reduce influenza virus transmission. There are fewer data to support the use of masks or respirators to prevent becoming infected.” This is basically the current thinking.
- The authors conclude there is no difference between N95 and surgical masks. They don’t say there is no effect, they say there is no difference in their effects. They specifically recommend wearing masks. And again, note, this study, like the others, only looked at the benefit to the wearer.
- The authors concluded there weren’t enough data to conclude whether N95 masks were better than surgical masks.
- The authors conclude that masks didn’t protect against viral infections. But then they cite a number of studies that show that masks were effective against SARS.
- The authors reported no difference between N95 and surgical masks. Again, they didn’t conclude that these masks weren’t effective; only that there was no difference in their effectiveness.
- Same as 6)
In summary, there are several problems with these studies: 1) all of these studies were carried out before the pandemic, and thus did not look at SARS-CoV-2 specifically; 2) most of the studies compared different mask types vs. each other, not vs. controls wearing no masks; 3) none of the studies actually considered whether masks would protect others from the person wearing the mask.
Rancourt points out that if there were a benefit of a mask, the N95 should be superior to a surgical mask. But that only addresses point 2), not the other two points. To address them, he basically goes to physics, arguing that the masks will not block fine aerosol particles, each of which may contain a number of viral particles capable of infecting someone.
He also cites a study indicating that viral infections increase during seasonal periods of low humidity, while decreasing during periods of high humidity. His interpretation of this is that high humidity results in larger droplets that fall more quickly out of the air.
He concludes, “if anything gets through (and it always does, irrespective of the mask), then you are going to be infected.” If that were true, then everyone within the same range of an infected person who is infecting some people would become infected. But we know this isn’t the case. Some people may have just as much contact with an infected person as other people who get infected (e.g., in a Chinese restaurant; a S. Korean office building; German households), but remain uninfected. They must be breathing in just as many particles, but don’t get infected. Why? Because it isn’t true that if anything gets through, you will become infected. This point is also underscored by the mean infectious dose Rancourt refers to. This is a dose that will infect half the people, but not all. This clearly implies that any reduction in incoming aerosol particles could potentially make the difference between getting sick and not.
Also, he again relies on studies of other viruses. There are no studies to my knowledge that show the minimum effective dose for SARS-CoV-2. Rancourt also doesn’t show data indicating how many viral particles may be contained in an aerosol particle. Theoretically, a 2.5 uM particle could contain several thousand SARS-CoV-2 particles, but that doesn’t mean that in practice it actually does. So when he says "the minimum-infective dose is smaller than one aerosol particle", this is speculative. Maybe, maybe not.
Finally, note that this link was removed from a research website. He claims he was censored. I don’t support censorship, and think Rancourt has a right to be heard. I welcome his views. But he also should be criticized.