By Maggie Fox
CNN
October 10, 2021
(CNN)There’s little doubt now — study after study, in real life and in lab dishes, in the US and elsewhere — that people’s immunity starts to wane just months after they finish the two-dose series of Pfizer Covid-19 vaccine.
While getting two doses of vaccine creates a strong immune response that reduces the risk of severe disease by more than 90%, the protection against milder and asymptomatic infections drops off gradually.
That’s why Pfizer has asked for and received US Food and Drug Administration authorization to add boosters for many people who are six months out from vaccination.