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Why it’s time for masks again (alas)

| Wednesday, August 25, 2021

Masks — no one likes them, they make communication hard, and yet they are about to become even more critical than ever. Locally, we enjoyed a July where the virus was (nearly) gone, and it seemed like it was back to old times (remember 2019?). Hospitalizations in our health district tell the story (you can look it up on the Indiana covid dashboard, click on health district 2 to find local values), where those hospitalized with Covid fell into single digits. What a difference a month makes: on Friday our district crossed into triple digits of hospitalization. That’s a lot of suffering, but it can be (and will be) a whole lot worse. Even our current rate of 16/100,000 (there are about 660,000 residents in our district) is much less than the statewide rate of 25/100,000 which is better than the national rate of 29/100,000 and is tiny compared to Florida at 79/100,000. Unless we take action, Florida is our future.

So why did this happen? It is a combination of behaving like it is 2019 again, fading effectiveness of the vaccines most of us have gotten, and the far more contagious Delta variant. The state vaccination dashboard tells the story (click on “breakthrough”). For the first five months (through mid-May) the ratio of cases/100,000 vaccinated and unvaccinated Hoosiers was only 10% or less. That’s why if you were vaccinated you didn’t really need to wear a mask under most circumstances (although it was never a bad idea), and this protection was the basis of the CDC recommendations last spring. With Delta and a few more months of fade that has changed, big time. The rate among vaccinated Hoosiers is now up to a third of the unvaccinated rate and still increasing — so even if vaccinated you have a much higher probability of catching Covid and passing it on to others than you did this spring, usually before you even have any idea you are infected, or if you never show symptoms at all. Another way of looking at it: if you remember how hard it was to contain the original version of the virus last fall, Delta is more than twice as contagious. Thus, Delta + vaccination is about as hard to contain as the original version was last fall. And Delta without vaccination is that much worse.

So why masks? Apart from vaccination, they are our best line of defense. That ordinary cloth mask you keep in your pocket (and hopefully wear properly on your face!) reduces the amount of virus you inhale by about 30%, but it reduces the amount you spray out by a factor of 10 or so. Why the difference? The stuff that comes out of your mouth and nose is mostly water, but this dries out almost instantly and floats around in the air, waiting to be inhaled by someone else. The change in diameter is roughly a factor of five, equivalent to the difference between a golf ball and a bowling ball — and a cloth mask does a great job at catching the big stuff. Because it is so much better at the “out” rather than the “in” everyone needs to mask up any time you are indoors, particularly in areas where filtered ventilation isn’t great or there are a lot of people. You would be amazed at the amount of stuff that comes out of your mouth when you speak; our lab did the flow visualization and mask testing last summer for Notre Dame and it looks really impressive in a laser sheet.

Vaccinations are still critical even if they aren’t giving us “sterilizing immunity” anymore (it was nice while it lasted and resulted in cases at ND basically going to zero this summer). It is still reducing infection by a factor of three, meaning you are three times less likely to pass the virus around (pretty good!), but the protection against hospitalization and mortality is better still. If you haven’t gotten vaccinated yet, please do so if at all possible: Delta is really, really nasty.

Professor David T. Leighton, Jr.

 department of chemical and biomolecular engineering

Aug. 22

The views expressed in this Letter to the Editor are those of the author and not necessarily those of The Observer.

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