Marty Makary is a professor at the Johns Hopkins School of Medicine, Bloomberg School of Public Health and Carey Business School. He is editor in chief of Medpage Today and author of “The Price We Pay: What Broke American Health Care — and How to Fix It.”

The latest guidance from Los Angeles County officials that fully vaccinated residents should once again wear masks to stop the spread of the delta variant is not just excessive; it also undermines vaccination efforts and perpetuates fearmongering.

As the United States has reopened, too many public health officials have held the fear of the unknown over people’s head. It’s a line of argument no one can overcome. Rarely can we ever guarantee that something bad won’t happen in the future — even in medical science. But we as practicing physicians routinely need to make decisions based on the best available information. We can’t just sit around in decision-paralysis based on uncertainty. In fact, doing so can cause harm.

Let’s consider what we know: Studies have found that the Moderna and Pfizer-BioNTech vaccines remain highly effective against the delta variant. We also have ample laboratory and clinical evidence that immunity to covid-19 is near-perfect at preventing covid-19 death from the delta variant and many other preceding variants. Even Rochelle Walensky, director of the Centers for Disease Control and Prevention, told NBC’s “Today” show this week that “if you are vaccinated, you are safe from the variants that are circulating here in the United States” (The CDC ignores the power of natural immunity, but the same could be said of those with natural immunity, too.)

Yet Los Angeles public health officials just scared off business travelers, conference organizers, tourists and others looking to get back to normal in the United States’ second largest city. What these officials are ignoring from their scientific calculus is that the No. 1 driver of health status in the United States has always been economic status. By sinking more businesses already on the brink of collapse, they are moving more Americans into poverty and worsening health outcomes, especially for mental health. The signs of this damage are already evident but will be described better in future studies that look back at the toll of excessive restrictions. Let’s stop making policy decisions based on outlier hypotheses that the delta variant will evade immunity when it has not.

One factor driving the fearmongering is that public health officials are staring at case numbers on their computers, oblivious to our new over-testing problem that is inflating case numbers. Specifically, the United States and Britain are routinely testing vaccinated people who are asymptomatic. This is ignoring CDC guidelines that say fully vaccinated people who have no symptoms do not need to get tested. This is based on the recognition that immune people who are asymptomatic might have a detectable virus particle in their nose, but it does not represent a transmission risk and does not cause illness.

This is especially true for the delta variant. The same mechanism that makes the variant more contagious (increased viral shedding and tighter binding to tissue) is believed to make it more persistent in the nose cavity lining. In medicine, we use the term “colonized” to refer an infection that persists at low levels and does not cause illness. A positive test in that situation is entirely different from a positive test in a sick person or asymptomatic carrier who is not immune.

Yet that testing is being done everywhere. Workplaces, social gatherings, schools and even hospitals are inappropriately using blanket universal testing policies that result in asymptomatic immune people testing positive even though they pose no substantive public health threat. That’s one reason cases numbers in Britain, where the delta variant is the predominant strain, have outpaced hospitalizations and severe disease. The other factor is a true increase in new illnesses in the nonimmune, who are more likely to be younger. But as we’ve seen in Sweden, declining death rates are not likely to budge even with a surge in cases among young people.

In addition, positive California cases will be artificially going up until July 2 due to a backlog in covid-19 case records. But our battle is not against positive test results; it’s against death and disability.

The public health community will likely need to ask Americans to wear masks in the fall or winter — and maybe every fall and winter — on a selective basis for people with upper respiratory symptoms or who were exposed to someone with symptoms. The CDC has already lost tremendous credibility with the public.

Sending an anti-science message on masking, as Los Angeles has done, threatens the effectiveness of other recommendations at a time when health officials need to win back public support. Masks should not be a political statement; instead, they should be used when there is a clinical benefit. Moving backwards on the return to normal for immune Americans could hinder public health efforts in the short-term and have long-term repercussions for trust in the medical profession.

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