Similar problems exist for other urgent Covid-19 policy questions, like whether employers should ever remove vaccine mandates and whether cities should remove vaccine verification for dining and other indoor activities when a certain percentage of the population is vaccinated.The truth is that science doesn’t have an answer for what level of Covid-19 transmission is acceptable in schools before and after masks are removed or what level is acceptable in communities before and after vaccine verification. Someone has to decide, and that decision will involve subjective assessments of the risks people will tolerate.Moreover, metrics that rely on public case numbers — such as the Centers for Disease Control and Prevention’s classification system for community transmission levels — may not be usable in the near future. Many states may eventually stop daily or weekly reporting of coronavirus case counts because so many people use at-home rapid tests, making public case counts inaccurate.In the absence of reliable data and metrics, our elected officials will need to make considered judgment calls. For example, my ideal situation would be for masks to come off in school when there’s universal vaccination among kids and adults in schools, hospitalizations have been stable or declining for at least four weeks and rapid tests and high-quality masks are abundant and free for anyone who wants one in school. But since we are unlikely to reach these levels soon, the next best option is for governors and mayors to decide what to do, as governors in New Jersey, Virginia and elsewhere have.Elected leaders should still consider data when making these decisions. They should start by asking public health officials: Is the overall burden of disease rising, and if so, could it overwhelm the health care system? Even if it’s not rising, are there gross inequities in disease burden by place or race that can be addressed, such as specific communities or facilities that require a targeted response?To answer, health officials will need to use an approach similar to how they measure flu activity. For the flu, public health officials acknowledge they cannot accurately count all community and hospitalized cases, so they monitor samples of the population for flulike symptoms, flu strains circulating and vaccine effectiveness. They make a composite estimate of flu activity and compare it with historical data. We can shift to this approach for Covid-19 and complement it with other promising approaches, such as wastewater monitoring.In most situations, however, elected officials need to operate in the far grayer area of interventions narrowly tailored to specific settings, like schools, nursing homes and jails. For each setting, officials need to consider whether the people in those places are vaccinated or are medically vulnerable, whether the building has optimized ventilation and whether there are high-quality masks and rapid tests available to all who want them — similar to the expectation that a building has abundant soap, water and paper towels for hand hygiene.