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Universal masking and limited close encounters with people infected with COVID-19 reduced the spread of the virus in a university setting, at least during a five-month period before the Delta variant took hold, according to a new report by the Centers for Disease Control and Prevention.

The report analyzed data from St. Louis University collected between January and May of 2021, when very few people on campus were fully vaccinated.

During that period, 265 of the university’s roughly 12,000 students tested positive for COVID-19. Those students named another 378 individuals on campus as close contacts. Of those, 7 percent reported only masked exposure to the infected, while 93 percent reported unmasked exposure.

Among the 378 close contacts, 30.7 percent -- 116 people -- subsequently tested positive for the virus. According to the report, the odds of a receiving a positive test result were “substantially higher” among close contacts who’d had unmasked exposure -- 32.4 percent -- than among those who’d been masked (7.7 percent). Only those with unmasked exposure were required to quarantine.

“Wearing masks and having fewer encounters with persons with COVID-19 reduced the odds of transmission in a university setting,” the report read. In addition, it found “no evidence of secondary transmission” from the two students who’d tested positive despite having only masked contact. “Universities opening for in-person instruction could consider taking mask use into account when determining which unvaccinated close contacts require quarantine if enforced testing protocols are in place.”