Longer interval between Pfizer jabs 'boosts antibody levels and T cells '

A new study carried out in collaboration with the University of Birmingham shows both short and long dosing schedules of the Pfizer Covid-19 vaccine generate strong antibody and T cell immune responses.

The study, led by the University of Oxford, in collaboration with the Universities of Birmingham, Newcastle, Liverpool, Sheffield, and supported by the UK Coronavirus Immunology Consortium, is one of the most comprehensive studies into the immune response generated by the Pfizer Covid-19 vaccine to date.

It found T cell levels are well-maintained and antibody levels are higher following a longer interval between the first and second dose of the Pfizer Covid-19 vaccine, despite a significant drop in antibody levels between doses.

Importantly, worldwide studies are showing that both the short and long dosing schedules lead to strong real-world protection against Covid-19, emphasising the importance of having a second dose of the vaccine.

The Protective Immunity from T cells to Covid-19 in Health workers study (PITCH) examined how antibody and T cell levels change over time following either a 'short ' (three to four weeks, average of 24 days) or 'long ' (6 to 14 weeks, average of 70 days) interval between the first and second dose of the Pfizer Covid-19 vaccine.

Of the 503 healthcare workers recruited to the study, 223 (44 per cent) had previously had Covid-19.

Key findings:

• For the longer dosing interval, antibody levels fell noticeably between the first and second dose when tested in the lab. In particular, neutralising antibody levels against the Delta variant were poorly induced after a single dose, and not maintained during the interval before the second dose. T cells were well-maintained between the first and second dose.
• Following two vaccine doses, neutralising antibody levels were twice as high after the longer dosing interval compared with the shorter dosing interval.
• After two doses, overall T cell levels were 1.6 times lower after the long compared with the short dosing schedule. However, after the longer dosing interval, a higher proportion of T cells present were 'helper ' T cells, which are important for long-term immune memory and helping generate antibodies to prevent infection.
• The longer dosing interval resulted in higher neutralising antibody levels, after the second dose, against the Delta variant and all other Variants of Concern tested.

The study results are being published as a pre-print on 'Cell Press Sneak Peak ' and have therefore not yet been peer reviewed.

Professor Paul Moss (pictured), Principal Investigator of the UK Coronavirus Immunology Consortium and Professor of Haematology at the University of Birmingham, said: “This is an important study that reveals how changing the interval between doses of the COVID-19 vaccine has a significant effect on the immune response generated.

“It also demonstrates the benefit of a team science approach that brings researchers together to understand key questions on the immunology of COVID-19. The UK Coronavirus Immunology Consortium has been incredibly successful in fostering new partnerships like this. ”

Alex Richter, Professor in Clinical Immunology at the University of Birmingham, said: “Real world data demonstrates the Pfizer COVID-19 vaccine is effective at reducing levels of serious disease, hospitalisation and death.

“There is benefit after one dose but two doses provides a much more robust response. Understanding the underlying immune response generated by different dosing schedules will help maximise future protection, tackle new Variants of Concern and prevent reinfections. ”