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A 12-Week Gap In Jabs Significantly Boosts Immune Response From Pfizer COVID-19 Vaccine


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockMay 21 2021, 15:13 UTC
Older woman getting vaccinated. Image Credit: Phawat/

Delaying the second Pfizer vaccines to 12 weeks significantly increases antibody responses in older people, the study found. Image Credit: Phawat/

The UK government took a gamble by changing the interval between the two COVID-19 vaccination doses needed, from the trial-tested three weeks to the untested 12-week gap, allowing for more people to have the first dose. The approach allowed a faster immunization of at-risk people, giving them some level of immunity but new research suggests this decision may have had an unexpected positive effect: it made the immune response more intense.

The preprint study (meaning it has not yet been peer-reviewed) has shown that among people 80 years and older, those who received the vaccination in a 12-week gap had an antibody response 3.5 times greater compared to those who had it at a 3-week interval. The team notes that while antibodies were higher, the cellular immune response – the fight inside the cell after they are already infected – was lower for the people on the 12-week interval.


“This is the first time antibody and cellular responses have been studied when the second vaccine is given after an extended interval. Our study demonstrates that peak antibody responses after the second Pfizer vaccine are markedly enhanced in older people when this is delayed to 12 weeks,” lead author Dr Helen Parry, NIHR Academic Clinical Lecturer at the University of Birmingham, said in a statement.

“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.”

This is the first direct comparison of the immune response between dose intervals in any age group, and looked at 80+ years people because as the first group to be vaccinated in the UK this age group holds the most data on the 12-week interval.  


“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," said corresponding author Paul Moss, Professor of Haematology at the University of Birmingham and Principal Investigator of the UK Coronavirus Immunology Consortium. 

“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.”


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