What's the Evidence Guiding CDC's Latest Mask Policy?

 Throughout the pandemic, we learned a lot about which drugs help and which don't. Steroids are of indisputable benefit when given to hospitalized patients who require oxygen or mechanical ventilation. Hydroxychloroquine does not work in a similar situation. Many things we thought might help, were found to offer no net benefit. We are much better off from having this knowledge.

Randomized trials were the scientific tool that allowed us to separate drugs that save lives from those that have no effect or even contribute to iatrogenic injury. Randomizing patients was the secret sauce to improving the care of people diagnosed with COVID-19, and I suspect future scientists will look back with admiration at the pandemic heroes: the trialists of RECOVERY and SOLIDARITY and other major randomized efforts.

When it comes to non-pharmacologic interventions such as mandatory business closures, mask mandates, and countless other interventions, the shocking conclusion of the last 18 months is this: We have learned next to nothing.

Yet, here we are again with CDC changing its mind on masking, but what new evidence is guiding the policy?

While CDC said vaccinated people with breakthrough infections from the Delta variant carry viral loads similar to the unvaccinated, they haven't yet shared any data on this, and this also doesn't negate the need for sufficient research into how and when mask mandates are effective. And no, I am not here to say that masking can't be an effective public health intervention. It may be, and people should mask-up when their local leaders tell them to. Instead, I am here to call attention to the need for evidence-driven policy.

Anyone who considers themselves a scientist should be embarrassed by our collective failure to generate knowledge, and this failure is once again looming large. The CDC is again recommending vaccinated people to wear cloth masks in indoor public spaces, at least in locations where COVID is surging. The CDC director calls this "following the science," but it is not. It is following the TV pundits.

Many studies have documented the flow of particles in and around masks, and countless studies have examined the differences between locations that implemented mask mandates and locations that did not. While this information is interesting, it is often conflicting, and worse, does not offer a sufficient basis for public health recommendations. Mechanistic studies are incapable of anticipating and tallying the effects that emerge when real people are asked to do real things in the real world.

Comparing places that implemented restrictions to those that did not is a fool's errand. The confounding variables abound: political valence, pre-intervention trends, other behavioral changes, and a host of other differences that are not easily adjusted for.

When it comes to drugs, for example, we would never accept this type of evidence. Knowing how hydroxychloroquine works in cells, and then comparing hospitals that used it versus those that did not would lead to confusion and ignorance. There are too many other factors. Only several well-done randomized trials adjudicate the uncertainty.

With the Delta variant and vaccination at play, the ignorance is even greater. Not only do we know very little if, and when, and under what circumstances mask mandates offer benefits, we know absolutely nothing about how this might operate in the face of a variant after individuals have been vaccinated. At what case rates are mask mandates most effective? Do they work only if you encourage surgical masks or is a cloth mask enough? Does this hold for vaccinated individuals in the setting of the Delta variant?

The CDC's guidance applies only to substantial and high transmission counties (50 daily cases or higher per 100,000 people), but again, there is no science that shows mandates work in these settings but not others. It is also a confusing and constantly changing metric to try to keep track of.

The CDC cannot "follow the science" because there is no relevant science. The proposition is at best science-y; a best guess based on political pressure, pundit anxiety, and mechanistic understanding.

The Second Order Effects

It is bad enough we have learned nothing about when and if mask mandates offer net gains, but this is compounded by the potential for second order effects.

If you start making vaccinated people mask again, will that be a disincentive for the "vaccine curious" to vaccinate? After all, they are already hesitant -- could they take from the guidance the tacit message that the vaccine is not that protective after all? P.S. -- The vaccine is that protective, and it retains amazing efficacy against Delta!

Will reinstating mandates be met by the same level of compliance as before? Will it lead to protests which have rocked other major global cities?

Worst of all is the likely scenario where the places with the political will to reinstitute mandates are probably liberal urban areas where vaccination rates are the highest and SARS-CoV-2 rates the lowest. Places that will be allergic to mask mandates -- southern, rural areas -- might be places where vaccination rates are the lowest and SARS-CoV-2 rates the highest. Ironically, the CDC's guidance might result in two different scenarios: excessive mask use where it won't help and inadequate mask use in places where it might help.

Let's also consider whether re-instituting masking will have even broader implications. Will it hurt the political fortunes of parties thought to support continued restrictions? Might the political ramifications have an impact on human health -- for example, through differences in funding for social programs?

The list of potential unintended effects goes on and on. Sadly, we know nothing here.

Science on Life Support

In a recent piece on public health, Monica Gandhi, MD, MPH, Stefan Baral, MD, MPH, and I argue that "in the beginning precaution is fine, but eventually public health must be driven by data." The amazing thing about COVID-19 is there are so many places where we know so much more than before, such as how to care for the hospitalized COVID-19 patient. But the tragedy is all the places where we know nothing more than when the pandemic began. Case in point: If and under what circumstances policy mandates help.

COVID-19 cases, which are rising now, will eventually fall, as seen in the U.K.. This is the inevitable dynamic of pandemic illness. One year from now, we still won't know if the CDC's action helped, hurt, or was merely coincidental.

When the history books are written about the use of non-pharmacologic measures during this pandemic, we will look as pre-historic and barbaric and tribal as our ancestors during the plagues of the middle ages. What the books won't capture is how, in the moment, our experts were simply so sure of themselves.

Vinay Prasad, MD, MPH, is a hematologist-oncologist and associate professor of medicine at the University of California San Francisco, and author of Malignant: How Bad Policy and Bad Evidence Harm People With Cancer.

https://www.medpagetoday.com/opinion/vinay-prasad/93803