On Wednesday Boris Johnson said he saw nothing in the current data to stop the planned lifting of Covid restrictions in England on 21 June. But he said questions remained over how much protection the current vaccines offered against the Delta variant, B.1.617.2.
What does vaccine effectiveness mean?
Vaccine effectiveness is given as a percentage and refers to how well a vaccine works in the real world, as opposed to the term efficacy, which relates to vaccines’ performance in trials. The figures are often given with respect to symptomatic disease, although other outcomes, such as infection, hospitalisation or death, can be used.