MEASURING STICK — Right now, most Covid prevention measures have been dropped, and the Omicron offshoot known as BA.2 is spreading. House Speaker Nancy Pelosi is the latest Washington boldface name to reveal she's caught it. So far, BA.2 isn't creating a surge of serious disease or filling up hospitals. But the D.C. cases are a stark reminder that virologists, epidemiologists and infectious disease experts still struggle, two years in, to put a solid number on a host of questions about Covid-mitigation tactics over the past two years. Among them: — How many lives were saved by mask mandates? By all the public health preventive steps combined? — How many people didn't get sick because bars were closed — or might not have gotten sick if more bars were closed? — What were the precise benefits of the social distancing measures that were introduced in March 2020? — Perhaps most controversially, what was the net benefit of closing schools? Working out how to measure the effectiveness of these types of preventive tools — called nonpharmacological interventions or NPIs — is important because a skeptical population could be called upon to follow them again when the next crisis hits — whether that's sooner, because of a curveball from BA.2 or another coronavirus variant, or later, from an altogether different threat. But coming up with those numbers is devilishly hard. "You are never going to be able to measure that precisely," said David Dowdy, an infectious disease epidemiologist at the Johns Hopkins Bloomberg School of Public Health. Scientists have studied masks, but they can't do a gold-standard, traditional study like a double-blind, random-controlled trial of mask wearing. For starters, people know whether they are wearing a mask! There have been other trials and studies, comparing mask wearers and non-mask wearers, but there are all sorts of variables that are hard to sort out with clarity — not everyone would be wearing the masks in the same settings, for the same time, and people who wear masks take other protective steps as well. That final point applies to studying other nonpharmaceutical interventions. It's difficult to study one NPI all by its lonesome, because people practice several prevention metrics — masking and avoiding crowds and working remotely and distancing and handwashing etc. — at once. And they are unlikely to do them consistently in ways that are easy to quantify and track. We can certainly see which states have had a higher death rate from the coronavirus, but it's hard to pull out precisely which nonpharmaceutical factors contributed — and vaccines of course are the single most powerful preventive tool. Public health officials know that the NPIs are imperfect — that's why they urge people to practice a bunch of them, because they work better together than one at a time. But imperfect doesn't mean worthless. But to emphasize that worth, scientists are still figuring out how to measure it. A lot of the ongoing study on NPI effectiveness is being done by modeling, more specifically something called "counterfactual" modeling. "We use computational models to simulate hypothetical outbreaks, and we can turn up or turn down different levels of mitigation, " emailed Natalie Dean, a biostatistician at Emory. Those models aren't whipped up in the ether. They are fed data from other studies and surveys — what Spencer Fox, the assistant director of the University of Texas Covid-19 Modeling Consortium, called "ground truth." But because people don't follow Covid-prevention measures with consistency, and more than one measure can be introduced at a time, it's hard to disentangle it all, Dean said. The pandemic also showed the holes in U.S. data collection for public health. Many of our decisions were based on studies from the U.K. and Israel, which have health data collection systems far better than our own; improving our data is really high on the to-do list, Fox said. Complicating matters is that while scientists draw conclusions based on a large body of data, some people cherry-pick studies for tendentious reasons. For instance, they may pluck out one small one — Sen. Rand Paul and other conservatives have pointed to one from Denmark — that found masks don't work, while ignoring a massive amount of other scientific literature that shows they are pretty darn useful. Dowdy likened that to pointing to a smoker who lived to be 100 and touting it as proof that cigarettes don't cause lung cancer. Welcome to POLITICO Nightly. Reach out with news, tips and ideas at nightly@politico.com . Or contact tonight's author on Twitter at @JoanneKenen.
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