Government strategy vindicated: Delaying Pfizer dose by 12 weeks three and a half times more effective  

Delaying the second dose of Pfizer by 12 weeks creates a three and a half times greater immune response in older people, a study has found, in an apparent vindication of government strategy.

The antibody response in people aged over 80 is three and a half times greater in those who have the second dose after 12 weeks, compared with a three-week interval, the study found.

Researchers said the study of 175 people, who were older than 80 and living independently, is the first direct comparison of the immune response in any age group for the different intervals.

While the Pfizer jab was originally authorised for a three-week interval between doses, several countries including the UK extended it to 12 weeks so a greater percentage of the population could receive one dose quicker.

The study, led by the University of Birmingham in collaboration with Public Health England, found that extending the interval to 12 weeks increased the peak spike-specific antibody response to the virus 3.5-fold compared with those who had the second vaccine at three weeks.

Although the peak cellular immune responses were lower after the delayed second vaccine, responses were comparable between the groups when measured at a similar time point following the first dose, researchers found.

They concluded that waiting 12 weeks to administer a second Pfizer jab potentially enhances and extends antibody immunity.

This is believed to be important in virus neutralisation and preventing infection.

First author Dr Helen Parry, National Institute for Health Research academic clinical lecturer at the University of Birmingham, said: "Sars-CoV-2 vaccines have been remarkably effective in providing large-scale protection against infection and symptomatic disease - but many questions remain regarding their optimal delivery for provision of effective and sustained immunity.

"This is the first time antibody and cellular responses have been studied when the second vaccine is given after an extended interval.

"This research is crucial, particularly in older people, as immune responses to vaccination deteriorate with age.

"Understanding how to optimise Covid-19 vaccine schedules and maximise immune responses within this age group is vitally important."

Corresponding author Paul Moss, professor of haematology at the University of Birmingham and principal investigator of the UK Coronavirus Immunology Consortium, said: "The enhanced antibody responses seen after an extended interval may help to sustain immunity against Covid-19 over the longer term and further improve the clinical efficacy of this powerful vaccine platform.

"Our research findings may be important in the development of global vaccination strategy as extension of interval of the second vaccine dose in older people may potentially reduce the need for subsequent booster vaccines."