Vaccination with two doses of the Pfizer jab stays highly effective against severe Covid - including the Delta variant - for at least six months, an analysis of US patients has found.
While previous data from clinical trials has shown jabs protect against hospitalisation, the study published in the Lancet measures one vaccine's effectiveness over time in a real-world setting.
Pfizer and healthcare provider Kaiser Permanente looked at records from 3.4 million residents of southern California, about a third of whom were fully vaccinated between December 2020 and August 2021.
After an average period of three to four months, fully vaccinated people were found to be 73% protected against infection and 90% protected against hospitalisation.