The Journal Gazette
Tuesday, April 06, 2021 1:00 am

By the numbers

Statistics show end of mask mandate premature

Christer Watson

The statewide mask requirement is ending today. I am not happy about that.

The argument for the mask requirement being statewide is straightforward. When the virus is widespread, people can be a risk to each other without knowing it. Symptoms are not a good guide.

Masks appear to reduce this risk significantly.

I strongly suspect this policy change is based on the hope that vaccines will stop the virus' spread. However, Indiana has only fully vaccinated about 17% the population.

That percentage is going up quickly and those with only one dose have some protection, but 17% is not high enough to slow the spread without help from masks and social distancing.

In explaining the policy change, Gov. Eric Holcomb discussed the virus' spread. He has often made good use of numbers to guide decisions through the pandemic, so I will assume a good faith position on his part.

For much of the pandemic, there have been three numbers that guided how to think about the virus.

The most basic number is hospitals' free capacity. When the pandemic was at its worst in some parts of the United States, hospitals could not provide full service to all their patients. There were not enough beds or ventilators or medical staff.

Although the fatality rate for the virus has always been hard to measure, it does appear that the fatality rate is higher when hospitals cannot give their full attention to those struck hardest by the virus.

So this criterion is really the most basic. Do local hospitals have enough free beds and personnel to handle those who are severely sick? I have always had a hard time understanding the different numbers used to estimate hospital capacity, but it appears that, statewide, we are in good shape.

The second and third numbers both aim to measure how widespread the virus is throughout the community. Unfortunately, this spread has also been difficult to measure consistently and accurately.

The most direct measure of the virus' spread has been how many positive tests there have been per day, commonly averaged over a week to smooth out the effect of weekends. The number also has to be adjusted for how many total people there are in a city, state or country.

That number, for Indiana, is currently around 19 daily cases per 100,000 people. Last summer, this number was around 10-20. During the worst of the winter, it was around 100.

There are some severe limitations to that number. For example, many people, especially the young, will have weak symptoms or no symptoms, and never get tested. Testing has, somewhat famously, not been consistently available to everyone, especially last summer and winter.

A second way, then, to measure the virus' spread is the percentage of virus tests that come back positive. This measure, called the positivity rate, is certainly much simpler.

I should admit my surprise at this number's usefulness. I would have thought it would depend too much on who happens to get access to tests. However, it appears to be useful since many experts appear to rely on it heavily.

For Indiana, the positivity rate is currently about 3%. Last summer, it was around 7%; during the worst of the winter, it was around 15%.

When people refer to following the science, I have always taken that to mean they would use a combination of the most useful numbers to guide our actions. I thought these three numbers were the most useful. The hospital number helps us know whether the fatality rate will be worse because our hospitals become overwhelmed. It represents the absolute bare minimum standard. The other two numbers help us know the spread of the virus.

When the governor announced the end of the mask mandate, he appeared to rely on the first of these numbers, hospitals' capacity. The second and third numbers, which measure the virus' spread, didn't get as much attention. That doesn't make any sense to me.

The virus is still out there, spreading. For this month, April, the vaccination percentage will not be high enough to slow the spread. Our two measurements of positive tests show that the virus is still common enough for it to be a real risk.

Masks are an effective way to slow the spread and reduce the risk.

For an example of what can happen, look to Michigan. The virus' spread there has now entered a new surge. Positive tests are about 60 per day (for 100,000 people), and the positivity rate is about 16%. That can happen here, and it can happen more quickly than politicians can react.

The mask mandate should be continued until all the numbers, not just one, show it is safe.


Christer Watson, of Fort Wayne, is a visiting assistant professor of physics at Purdue University Fort Wayne. Opinions expressed are his own. He wrote this for The Journal Gazette, where his columns normally appear the first and third Tuesday of each month.

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