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Should You Wear a Mask?

The short answer for the general public: it's up to you. The Surgeon General says it's a bad idea for most people who aren't sick because people touch their face more when they're wearing one. Others say it keeps people from spreading germs.

Lately, this silly graph has been bouncing around the internet:


Let's take some lessons from dietary science and apply them here.

Correlation isn't Causation 

One wag put up a graph that said, instead of Masks and No masks, Bubble Tea and No Bubble Tea. That must be it--let's all drink bubble tea!

Fun with Y Axes

Note the Y axis is cumulative cases, not cases per million population. Singapore and Hong Kong are city-states with populations of 5.8 million and 7.5 million. Those are small populations as far as countries go, so we'd expected them to have low cumulative numbers of cases.

Also note that these are cases, not deaths. Spain and Germany are in almost the same place on the chart, and yet Spain's deaths per million from COVID-19 are more than 20 times that of Germany at this writing. Most cases have mild or no symptoms--and nobody really knows how many cases there are.

Confounding Variables

Hong Kong suspended border crossings around early February. 
Singapore and Hong Kong are both the tropics, where COVID-19 hasn't been as common.
These are more reasons we'd expect them to have low numbers.

Does this Association Hold Up Elsewhere?

If mask wearing by the general public were effective in preventing COVID-10, we'd expect to see lower mortality rates from the regular flu in mask-wearing countries circled on the graph above, since the flu is spread the same way COVID19 is according to the CDC:
People with flu can spread it to others up to about 6 feet away. Most experts think that flu viruses spread mainly by droplets made when people with flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. Less often, a person might get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose, or possibly their eyes. [emphasis added]
But according to a study in the Lancet, flu mortality rates are all over the place. The figure is "Influenza lower respiratory tract infection mortality rate per 100 000 for all ages, 2017."


Deaths per 100,000 from flu lower respiratory tract infection:

Asia Pacific (High Income) 4.0

Japan: 5.1
South Korea: 1.6
Singapore: 3.0

China: 0.8

North America (High Income) 1.1

US: 1.1
Canada: 0.8

Western Europe: 2.1

Spain: 1.6
UK: 3.7
Italy: 0.8
Germany: 1.7
France: 2.2

I've added a few selected countries that are part of the averages for the regions. China's low figure of 0.8 seems low, considering it's typically the source of the flu. The rest of the figures are higher than the US and Canada. Those countries have an advantage of being mostly uncrowded. But there's no pattern within the group of mask-wearing countries--the range is 1.6 to 5.1 and whatever the figure for China really is. Which leads me to the last point.

Masks don't seem to be containing the flu in China. 

Conclusion

To be fair, the flu associations above aren't causal and probably have their own confounding variables. It may be that wearing a mask does help someone in the general population, but nothing here shows it.

If you're taking care of someone with COVID19, you should wear a mask. If you might be sick and can't avoid going out, or you have to be in an area where you can't avoid coughing or sneezing on others, then wear a mask. Find out how to wear it correctly. Or make your own and wear it if you like. But so far, I'm not convinced the general public, especially those of us still at the office who'd have to wear a mask all day, every day, for it to do any good, need to wear one.
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