AstraZeneca vaccine followed by Pfizer dose is 'highly safe, effective': Study
The Combivacs study, run by Spain's state-backed Carlos III Health Institute, found the presence of IgG antibodies in the bloodstream was between 30 and 40 times higher in people who got the follow-up Pfizer shot than in a control group who only received one AstraZeneca dose.19-05-2021