One of the largest teachers unions in the country—the Chicago Teachers Union—warned that the COVID-19 Delta variant or other new strains of the virus may pause in-person instruction. In a letter (pdf) to Chicago Mayor Lori Lightfoot, the union said that “new pandemic variants pose immediate threats to the health of all Chicagoans, but especially our unvaccinated student population,” while praising Illinois Gov. J.B. Pritzker’s mask mandate at schools. The union then made demands for upgrades to schools’ ventilation systems, a testing plan for vaccinated and unvaccinated staff and students, full-time contact tracers and nurses “in every school building,” and “maintenance of criteria and health metrics based on COVID prevalence to pause in-person instruction.” Throughout the pandemic, in some major metropolitan areas, there has been a back-and-forth battle between teachers unions, parents, and at times, local officials over when to restart in-person classes. The unions have faced criticism for essentially dragging …