Air purification lessons from measles

In the year 2000, the United States had no measles cases. Last year, the CDC reported 1,282 cases of the disease, many of them in school- aged children. Unlike COVID- 19, there is a viable, widely used vaccine against measles, and a group of researchers from Harvard recently determined that the vaccine is far more effective at controlling the spread of the disease than any other mitigation efforts. “Our results highlight the primary importance of vaccination for reducing the risk of measles transmission among students,” researchers wrote, though they did say that “additional and significant risk reduction can be achieved through compartmentalizing students and enhancing building ventilation and filtration systems.” To do this work, researchers had to create a general model of schools, taking into account the wide range of air filtration and ventilation in various school settings. For example, they found that most primary schools in the United States, 63 percent, had ductless ventilation systems with air filters. Most secondary schools, too, had the same sort of ventilation systems in place, though a smaller percentage — 54 percent. Perhaps consequently, the transmission risk of measles, which is airborne, was found to be higher in secondary schools than it was in primary schools. The results of the study are clear— vaccination is the most effective way to limit transmission of the measles virus. But taking vaccination out of the equation, air purification and filtration actually makes a difference. Comparing various types ofHVACsystems shows schools with ductless- with- air- filter systems have the lowest transmission risk of measles, while the risk is highest for schools with ductless- without- air- filter systems,” the study says, finding “a large difference among the effectiveness of various control strategies and the selected infection control approaches can reduce the average number of infected cases up to 56 percent when a combination of advanced air filtration, ventilation and purification approaches was adopted.”