Two doses of either the vaccine made by Pfizer PFE, -0.43% and BioNTech BNTX, -1.06% or Oxford-AstraZeneca AZN, +0.92% vaccines provided a similar level of protection to prior natural infection when the Delta variant was dominant, the U.K. Office of National Statistics said Monday. Vaccination significantly reduced the risk of people testing positive during both the Alpha-dominant period and the Delta-dominant period, but effectiveness was reduced in the Delta-dominant period compared with the Alpha-dominant period.