I never heard the term sterilizing immunity until just the other day, but the concept was deeply embedded in my own assumptions. I assumed that all immunity is “sterilizing,” meaning that disease and infection are both prevented. It turns out that immunity can also be “non-sterilizing,” meaning that while disease is prevented infection is not.
I find the distinction useful for making sense of media reports on Covid-19 vaccines. For example, when a journalist talks about the “efficacy” of a vaccine you can usually interpret that as referring to its sterilizing effect. In fact, effective immunity — also called practical immunity — is synonymous with non-sterilizing immunity.
The Covid-19 vaccines confer non-sterilizing immunity. That’s much simpler to understand than the idea that no vaccine is perfect.