By coincidence, in November 2019 I did an investigation into the question – does wearing a facemask reduce the risk of transmitting or getting a respiratory infection? I was in Australia at the time and noticed that their large Asian population frequently wore facemasks in public. It seemed odd, and my initial hypothesis was that this was likely a cultural behavior without supporting evidence. I was surprised to find, when I reviewed the primary literature at the time, that I was wrong. In fact, masks do work, in certain circumstances.

The basic concept is simple – when you breath, talk, cough, or sneeze you exhale tiny droplets, and if you have a viral respiratory illness those droplets are crawling with virus. Masks reduce the spread of those droplets, and otherwise you are basically spraying everyone with a shower of viruses. They are less effective at protecting the wearer, but they do reduce the risk of getting sick as well. However, that reduction is only statistically detectable if you are in a high-risk situation to begin with. This includes being in the same room with someone who is sick, or being in a crowd during an epidemic. Out in the general population not during an epidemic the baseline risk of catching a virus is low, and so there is no statistically detectable benefit from wearing a mask.

This conclusion was based on information available before anyone ever heard the word “Covid-19”. Who would have thought at the time that this entirely scientific question would become so political so fast? The efficacy of mask wearing suddenly became a very important question, so now we have much more research, and some specific to SARS-CoV-2. This research has raised our confidence that masks do, in fact, have efficacy (science-speak for “they work”), but has also drilled down to greater detail. Where does the research stand now?

I last reviewed this evidence in January of this year – you can read that article for details and links, but let me summarize the findings quickly here. There are essentially three kinds of evidence we can look at – do masks reduce the spread of droplets, do they prevent individuals from getting sick, and how well do they work as public health policy. All three types of evidence point to the conclusion that mask wearing is effective.

Here is the most recent meta-analysis of published data, from August 2021, which finds:

Given the body of evidence through a systematic review and meta-analyses, our findings supported the protective benefits of MFMs [medical face mask] in reducing respiratory transmissions, and the universal mask-wearing should be applied-especially during the COVID-19 pandemic. More clinical data is required to conclude the efficiency of cloth masks; in the short term, users should not use cloth face masks in the outbreak hot spots and places where social distancing is impossible.

One aspect of the evidence that is important to point out is that it clearly shows a “dose response” effect – N95 masks are better than hospital masks are better than cloth masks. If masks were not helpful then better masks would not work better.  Here is another recent study which shows that N95 masks are better at reducing the spread of aerosolized particles than cloth masks. In fact, cloth masks do not prevent their spread at all, just redirect the stream out the edges of the mask. N95 masks are tighter fitting and filter out the virus (in fact, 95%, hence the N95).

It is nothing less than shameful that we are still bogged down in the basic question of whether or not wearing a mask during a deadly and increasingly infectious pandemic is effective. The science is in – masks work. We need to now focus on maximizing the effectiveness of wearing a mask – which masks work better? Given the increased infectivity of the delta variant, which now makes up 98.8% of COVID cases according to the CDC, everyone needs to be reminded of the importance of wearing masks in public. Further, we should be focusing efforts on making sure everyone knows which masks are better and how to wear them properly.

Cloth masks are problematic, because low quality masks offer dubious protection. A high quality cloth mask should have multiple layers, at least three, and should cover the entire nose and mouth with a good fit. Ideally they would have a wire to pinch around the nose for a tight seal. Some may even have pockets to insert filters. Thin cloth or neck masks are useless. If you are unsure about the adequacy of your mask, then wear two.

Hospital masks are clearly better than cloth masks, and they are easy to obtain. There is no longer an issue of a mask shortage, and they are not expensive. You can still wear your cool cloth mask over the hospital mask if you like, and the extra coverage is likely advantageous. But N95 masks are best. If you are in a hot spot, need to be in a risky situation for some reason (for your job, for example), if you are vulnerable or live with someone who is, consider upgrading to an N95 mask. The primary difference is that they not only protect against droplet spread but also aerosolized spread. These are also widely available, although they are a little more expensive (but still only about a dollar a piece).

This is important – if you are going to double mask with an N95 mask, the N95 goes underneath. If you wear it over a cloth mask that ruins the seal and reduces the efficacy of the N95 mask.

I know this is all tedious. We were hoping that by now we could start to relax our pandemic protocols. We had a brief glimpse of that over the summer, but that glimpse is over. Earlier in the year I wrote about the fact that we were essentially in a race between achieving herd immunity through vaccination and the appearance of more infectious variants. Well – we lost the race. That is to say, anti-vaxxers and the vaccine hesitant lost the race for all of us. There is no way to sugar-coat this. We had a window of opportunity, and now the window is closed, and it is entirely due to people who refused, against all evidence, to get vaccinated. The delta variant is now surging, vaccine efficacy is waning, and children are now being affected in greater numbers.

Further, the delta variant will likely not be the end of this pandemic. More variants are likely to come, because we are allowing this pandemic to simmer along, happily mutating new versions of the virus. The delta variant is now the baseline. Many experts believe it is unavoidable that COVID will become endemic, one more disease we will have to learn to live with, like the flu.

This means we need to keep the pandemic protocol knowledge and skills that we learned. We cannot go back to pre-pandemic times. Mask wearing and social distancing is still important, and in fact more important. The delta variant is more infectious, and our protections have to be a bit tighter. We need to make sure that everyone knows that masks work, and also which masks work best. We need to be a mask-literate society.