A study led by the University of Birmingham in collaboration with Public Health England found that antibodies against the virus were three-and-a-half times higher in those who had the second shot after 12 weeks compared with those who had it after a three-week interval. Most people who have both shots of the vaccine will be well protected regardless of the timing, but the stronger response from the extra delay might prolong protection because antibody levels naturally wane over time. Dr Helen Parry, a senior author on the study at Birmingham, said: “We’ve shown that peak antibody responses after the second Pfizer vaccination are really strongly boosted in older people when this is delayed to 11 to 12 weeks. There is a marked difference between these two schedules in terms of antibody responses we see.”