So far, little data has existed on the comparative safety of Covid vaccines, and the immune responses they stimulate as a third dose.
Data from these studies are expected soon.
While AstraZeneca vaccine is administered in more than 180 countries, Pfizer is available in more than 145 countries.
The phase 2 trial included 2878 participants, all of whom were in good health at the time they were recruited from June 1-June 30, 2021.
We note that Vaxzevria was developed by AstraZeneca in partnership with the University of Oxford.
Side effects from the booster doses are similar to those experienced from earlier doses, though some data suggest the effects after a booster may be milder than after the second dose.