The biology behind ‘breakthrough’ cases and the confusing CDC mask guidance.

...herd immunity may prove difficult to achieve unless more people get infected and develop natural immunity of both types. Given the dangers of infection, officials are rightly reluctant to encourage actual infection, and loath to mention its benefit in conferring mucosal immunity. But we shouldn’t shun people who have recovered from Covid. Vaccine mandates for in-person interactions—whether imposed by governments, employers or businesses—should make exceptions for the previously infected, who thanks to natural mucosal immunity are likely at less risk than never-infected vaccinated people of spreading the virus to others.

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