As game-changing as the Pfizer vaccine (and Moderna‘s equally effective mRNA-1273 vaccine) may be in affording protection against the COVID-19 illness, the results do not reflect complete „sterilizing immunity.“

This is the type of immunity that completely prevents a disease-causing pathogen like COVID-19 from establishing an infection. Sterilizing immunity differs from effective immunity in that the latter can prevent illness but still lead to asymptomatic infection.