As part of recommending the mandate, OSHA re-examined the risks of and associated with coronavirus reinfection.
The agency concluded that while "the science is evolving," the current data is not enough to save individuals from "grave danger" of exposure to and reinfection from the coronavirus.
"A considerable number of individuals who were previously infected with SARS-CoV-2 do not appear to have acquired effective immunity to the virus," OSHA wrote in a lengthy report, citing research conducted by multiple studies over this past summer. "The level of protection afforded by infection-induced immunity appears to depend on the severity of individuals' infections."
One study from Greece compared immunogenicity between vaccinated healthcare workers and unvaccinated patients with natural infection: The researchers found unvaccinated individuals developed immunity that corresponded with the severity of their infection, with the vaccine providing protection 1.3 times greater than the most critical infections, 2.5 times greater than moderate cases and 10.5 times greater than asymptomatic or mild infections.
This correlates with other studies, such as a study from the Centers for Disease Control and Prevention (CDC) that found unvaccinated individuals were twice as likely to face reinfection as were vaccinated individuals.
The vaccine also may provide greater protection against future infection since some studies indicated that a person with natural immunity as the effective immunity of an uninfected individual with one dose of a two shot vaccine regimen.
OSHA acknowledged some studies found natural immunity showed a significant level of protection against reinfection, but "these studies suffer from methodological limitations that render them inconclusive about the level of immunity conferred by infection."