COVID: No politics, only science
By: Josh Townley
Tags: Masks, Covid-19, Evidence, Science

Is COVID really that dangerous?

First of all, why are we wearing masks in the first place? Is COVID really a bigger threat than seasonal flu or other common diseases?

You may have seen numbers floating around that around 99% of COVID cases aren’t serious, or are asymptomatic, a claim that seems to have originated from Donald Trump, but is still commonly quoted in Facebook groups or in YouTube comments. This seems like an odd argument to be spreading around for several reasons. Firstly, if we look at the official number of confirmed cases and deaths in Australia (on 12/9/21) we see 71,955 and 1,084, respectively. This gives a case fatality ratio (CFR) of around 1.5%. It’s around the same if we look at the total cases and deaths across the world (in the US, it’s currently about 1.6%). Either my maths is wrong, or some of those deaths are considered ‘non-serious’. (Note that the CFR varies with age, and may be more like 10–40% in elderly populations)

Secondly, even if we say the mortality is 1% or below, and expose the majority of the world’s population, we’re still facing tens of millions of deaths. By any measure, that is a catastrophic outcome, and one we should do everything in our power to avoid.

For the sake of comparison, influenza (flu) and pneumonia kill about 15.2 people per 100,000 infected in the US, which works out to be 0.0152%. A study out of France found that the in-hospital mortality rate for adolescents aged 11–17 was ten times higher for COVID-19 than for flu, so even if you’re young and healthy, COVID is much more dangerous than the flu.

But could COVID really infect most of the population before running out of steam when we reach natural herd immunity? Consider this: The R0 value for the 1918 flu was around 2, which means each infected person could infect 2 others — enough to cause exponential spread of the virus. (The 1918 influenza strain is estimated to have killed between 20 and 50 million people, with a CFR of around 2%). The R0 value for the original COVID strain was 3; HIV and SARS each score a 4. The R0 value for the delta strain of COVID is thought to be around 5, and could be as high as 8.

Let that sink in for a moment before we continue.

Are masks effective at stopping the spread?

I think we can all agree on one thing: wearing masks all the time sucks.

It’s a pain having to remember them every time we go out; they make it more difficult to breathe; they can cause irritation or acne; and they never fit my ears properly, making them stick out. But like it or not, mask mandates are now common in many parts of the world as a measure to help control COVID-19 transmission.

When questioning whether masks make a difference, there are really three questions we need to consider:

Do masks help protect you from contracting the virus from someone else? Do masks help prevent you from spreading the virus to others? Does widespread mask use lower the infection rate in the wider population?

The use of face masks was common in surgical practice and hospitals long before the arrival of COVID and can be traced back to the early 20th century, although for many years some surgeons rejected the idea of wearing face masks or even gloves on the grounds that they were ‘iritating.’ With our modern knowledge of diseases transmitted through droplets produced when coughing, sneezing or even simply breathing, however, it seems perfectly logical that masks covering the mouth and nose should help prevent transmission, so I was surprised when I discovered the state of the research before the current pandemic was not as convincing as I assumed.

Unsurprisingly, the pandemic triggered a wave of new research into the effectiveness of face masks so we’ve gained a lot of new information over the last two years. However, most of this evidence is from observational studies, laboratory studies or mathematical modelling. The best and most compelling evidence comes from randomised, controlled trials (RCTs), where people are randomly assigned to one of two groups, one of which uses the intervention (in this case, masks) and the other group does not. But for obvious reasons, it’s very difficult to get ethical approval for these types of studies when facing a deadly pandemic. There is one, however, and it could help answer our first question.

1. Do masks help protect you from contracting the virus from someone else?

Danish researchers conducted a RCT involving around 5,000 people to discover whether wearing a mask reduced your chance of contracting the virus. The study was designed to test the theory that masks reduce infection in the wearer by 50% (this is important when considering the statistical power of the trial).

They recorded 42 cases of COVID-19 in the mask group and 53 cases in the control (no mask) group, but even though that seems like masks made a small difference, the numbers were not considered statistically significant. That means when you account for the uncertainty and margin of error, the authors are saying that masks didn’t offer any detectable protection for wearers. However, there are a few important caveats to note about this study:

The researchers were looking for a 50% reduction, and powered the study accordingly. If they were to look for a smaller reduction, and used a much larger group of people, they might have been able to show a statistical difference (or it might have shown more conclusively that there was no difference)

This study was conducted under particular circumstances — with modest community infection, some social distancing and low general mask use. Under different conditions, the result might be different.

So, cutting to the chase, do masks protect you from contracting the virus out in the community? The evidence seems to say, ‘unlikely.’

2. Do masks help prevent you from spreading the virus to others?

Some people have cited the Danish study as proof that masks do not offer any benefit, but this only shows one side of the question. Since mask wearing in the general population was low (at the time of this study), it doesn’t give any indication about the role of masks in source control — that is, reducing the chances that an infected person can transmit the virus to others. To answer that question, we need to look elsewhere.

We all know that the SARS-CoV-2 virus is spread through liquid droplets that are released when we cough, sneeze, speak or even breathe, and for this reason, transmission most commonly occurs when people are in close contact. Larger droplets, which can carry a higher viral load and are therefore potentially more infective, are ejected from coughs and sneezes and possibly speaking. However, because of their size they tend to travel straight forward and quickly fall to the floor or other surfaces. Smaller droplets (microdroplets or aerosols), which carry a smaller viral load and come out in our breath, have the potential to remain in the air for longer periods of time, especially when the humidity is high or ventilation is poor. But in order to become infected, you would need to breathe in a larger number of droplets to reach an infective dose, making it a less efficient route.

I’m going to spoil the ending here by telling you there is no definitive answer for exactly how much protection masks offer when it comes to slowing the spread of COVID-19, and that’s mainly because it would be unethical to conduct the experiments needed for a conclusive answer. I believe, though, that there is more evidence in favour of mask-wearing. When I went hunting for evidence to show that masks as a form of source control offered no benefit, I ended up on YouTube, where I encountered videos like this.

By using a vape pen as a demonstration to visualise how easily aerosols can escape a mask, this doctor seems to provide a compelling case that they are effectively useless. In some circumstances, he might be right. If we consider a small enclosed space, with no ventilation or recirculated air, where an infected person was present for an extended period of time, the concentration of viral-laden microdroplets would steadily increase to the point where infection becomes almost certain, regardless of who’s wearing a mask. But that’s a worst-case scenario.

Workplaces and other indoor spaces are actively trying to improve the ventilation as a way to limit aerosol buildup and transmission. In outdoor settings, or in well-ventilated spaces, the difference between redirecting your breath up or away from someone nearby, rather than spraying a cloud directly into their face could be significant.

Researchers who have modeled airborne transmission, taking into account real-world studies and so-called ‘super infective’ subjects, suggest that good ventilation and mask wearing together may reduce individual infection risk by a factor of 5–10.

Systematic reviews like this and this, found that the evidence overall supports the use of masks, but acknowledge that more robust evidence is still needed.

And that brings us to what is arguably the main question surrounding mask use.

3. Does widespread mask use lower the infection rate in the wider population?

One of the often-cited resources by mask skeptics is the Swiss Policy Research website, which seems to mount a convincing argument that masks are ineffective as a public health measure. They summarise a number of studies and paraphrase the conclusions, and although most of what they say is not wrong, it is highly biased, unbalanced and misleading. They also present a series of charts showing COVID-19 cases on a timeline with markers showing when mask mandates were introduced, and point to the fact that case numbers continued to climb despite widespread mask use.

Source: Swiss Policy Research — https://swprs.org/face-masks-evidence/

These are misleading for a couple of reasons. Firstly, mask mandates are often introduced as case numbers are starting to spike as a means to help slow the spread, so it’s not surprising that we see these sorts of patterns. Secondly, they are uncontrolled observations that don’t give any information about what might have happened if mask mandates hadn’t been introduced. Even the overlaid charts that show two different regions (e.g. North Dakota vs South Dakota in the image above), don’t account for the numerous variables like population density, age, testing rate, vaccination rate etc. so don’t provide a meaningful comparison.

It’s true that there is no definitive, high-quality evidence that shows masks are an effective public health measure. The literature as a whole suggests that they are only somewhat effective as a form of source control. That they may offer a small benefit when it comes to limiting transmission.

However.

They don’t need to be highly effective to make a difference. It’s not all or nothing. When you have a disease with an R0 greater than 1, that spreads at an exponential rate, any measures that decrease that spread also have an exponential effect. Earlier I mentioned that the R0 value of the delta strain of SARS-CoV-2 is thought to be around 5. Suppose through widespread mask use, we limit the number of people an infectious person could infect, and that number was reduced ever so slightly to 4.8. Those 4–5 newly infected people go on to infect another 4–5 each, and so on. How would that play out? Surely a difference so small it could be attributed to a rounding error would be insignificant. A simple spreadsheet calculation can give us an idea:

That’s a difference of 3,273,119 infections over time (rounded to whole numbers). Close to 50,000 lives saved, using a CFR of 1.5%. Obviously, there are many more variables in the real world and I’m not saying that masks alone reduce the R0 by that much (although they might), but the point is that even a very small difference over time can become highly significant.