Did the mandate help?

Leadership from the Shelby County Health Department is crediting the mask mandate for a reduction in the infection rate. Below is a clip from today’s Joint Covid Task Force news conference.

“There have been two time periods where we had… the reproductive rate pushed below one. The first was last July, after the initial face-masking orders went into place across the county and throughout the City of Memphis, and that – just simply wearing the mask – drove the reproductive rate of the virus down by interfering enough with the transmission of the virus that Rt (or reproductive rate) dropped below one.” – David Sweat

Unfortunately, there are a few problems with this interpretation.

First, the infection rate began falling in the middle of June.

As you can see from the yellow line, the early peak of the reproductive rate arrived a little more than halfway between June and July.

Mr. Sweat chooses careful wording to draw our attention to the point indicated by the yellow circle. But it’s clear the 1.0 threshold was crossed in the middle of a downward trajectory that stretched about a month.

Second, Sweat provides no explanation for why the mandate stopped working as well in August, what caused the rate to fall once again between October and March, nor what is driving the increase now.

The mask mandate has not been lifted or significantly altered since it was implemented in July. If it was responsible for the (continued) decrease last summer, why didn’t it prevent new increases in the second half of the year or in recent days?

Third, Tennessee’s reproductive rate has for the last year been nearly identical to Shelby County’s, despite the lack of a statewide mask mandate.

While Shelby County’s numbers are also reflected in Tennessee’s, we would expect these lines to diverge if mask mandates had any significant impact.

And finally, all of these numbers flow from the assumption that we’re detecting significant changes in the number of people infected.

But that assumption is complicated by the finding that known cases of COVID-19 represent only a fraction of total infections, as reported today by the Daily Memphian and earlier by the Commercial Appeal:

The study found that about 27% of the population had antibodies for the virus. If that number held throughout the entire population, that would mean about 270,000 people have actually been infected with COVID-19 in Shelby County.

As of Friday, there had been 89,960 known infections in Shelby County, meaning the local data could be off by a factor of 3. Experts such as Jain have always estimated that the true number of infections was much higher than the known infections. 

If we are only aware of a third of what’s happening with the virus, it’s possible that what we thought were significant ups and downs were just statistical noise.

To be fair to the other side of the argument, I will take note of a report the CDC released last month crediting mask mandates with reducing case growth rates by between 0.5 and 1.8 percent.

Even if we assume the study is accurate, though contradicted by numerous examples, it still comes down to a philosophical question:

Should (unelected) government leaders hold the authority to impose a mandate, for an indeterminate period of time, on an entire population, more than half of whom now carry at least some level of immunity, for a chance of improving one health outcome by less than 2 percent?

My answer is no.

Highly effective and safe vaccines are now available to any adult. If health officials want more shots in arms, they should stop talking down their effectiveness and start promoting their benefits.

Every minute the health department spends defending masks is a minute it could be spending reassuring people about the benefits of the vaccines, some of which authorities have even paused. If they are worried about vaccine hesitancy, they will find the answer by taking a look in the mirror.