Consequently, extending the administration of a second dose to 12 weeks could potentially enhance and extend antibody immunity, say the authors – and could even reduce the need for booster shots.
The Pfizer/BioNTech vaccine’s Phase 3 trials were based on 3 weeks between doses: a gap maintained for mass vaccination campaigns some countries like the US. The UK, however, chose to expand the gap to a 12 week interval to allow a higher proportion of the population to receive one vaccine dose quicker.
Antibody and cellular responses
The pre-print study, led by the University of Birmingham in collaboration with Public Health England and supported by the UK Coronavirus Immunology Consortium, looked at 175 people aged 80+.
A total of 99 people had the second vaccine at three weeks; while 73 had the second dose at 12 weeks.
Participants were tested after the first vaccine dose and then again two or three weeks after the second dose.
The study found that extending the second dose interval to 12 weeks increased the peak SARS-CoV-2 spike specific antibody response 3.5-fold compared to 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.
In relation to the cellular (or T cell) immune response, 60% of participants in the three-week interval group had a confirmed cellular response at two to three weeks following the second vaccine, but this fell to only 15% eight to nine weeks later.
In the 12 week group, only 8% showed a cellular response five to six weeks after the fist dose; but 31% of participants showed a cellular response two to three weeks after the second vaccine. Research is required to further explore these variations in responses, say the authors.
“This is the first time antibody and cellular responses have been studied when the second vaccine is given after an extended interval,” said Dr Helen Parry, National Institute for Health Research Academic Clinical Lecturer at the University of Birmingham. “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.
“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.”
Paul Moss, Professor of Haematology at the University of Birmingham and Principal Investigator of the UK Coronavirus Immunology Consortium, added: “ 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.”