But as researchers looked at the results, they found that the delay turned out to have another major benefit. “The bigger the gap you can leave between vaccines the better the immune response”, Cambridge University consultant clinical virologist Dr Chris Smith told RNZ. “Twelve weeks was de rigueur.” Same message from a June 2021 study from the University of Birmingham and Public Health England: “Antibody response in people aged over 80 is three-and-a-half times greater in those who have the second dose of the Pfizer Covid-19 vaccine after 12 weeks compared to those who have it at a three-week interval.” “Data from clinical trials shows that the efficacy was higher when the second dose was given at, or after 12 weeks.”