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COVID-19 study supports flexible intervals between Pfizer and Oxford/AstraZeneca vaccine doses


Southampton researchers have helped show a greater immune response occurs if two doses of the Pfizer-BioNTech or Oxford-AstraZeneca vaccine are given 12 weeks rather than four weeks apart.


The latest findings from the University of Oxford-led Com-COV study, show leaving a longer gap between vaccine doses may result in better immunity against COVID-19.


The results, published in the Lancet Respiratory Medicine, support flexibility in the time left between the first and second doses for these two COVID-19 vaccines. This could be helpful in countries where vaccine supply may be inconsistent.


The study was led in Southampton by Professor Saul Faust, Director of the NIHR Southampton Clinical Research Facility.


Mix-and-match approach


The study, supported by the National Institute for Health and Care research (NIHR), trialled two doses of the Pfizer-BioNTech vaccine, two of the Oxford-AstraZeneca vaccine, and mixes of both.


A standard two-dose Pfizer-BioNTech or Oxford-AstraZeneca vaccine schedule showed a greater antibody increase when given at a 12-week interval, compared to a four-week interval.

In mixed schedules, only Pfizer-BioNTech followed by Oxford-AstraZeneca recorded a significantly stronger immune response in the 12-week versus four-week interval groups, and only at 28 days following a second dose. This lasted for six months after the second dose.


No safety concerns were raised in the study of 730 participants. They were recruited across eight sites, including the NIHR Southampton Clinical Research Facility.


Informing COVID-19 vaccine schedules


The Com-COV study first reported robust immune responses following mixed Oxford/Pfizer schedules in June 2021.

Data from the study also informed the UK’s 2021 winter booster programme.


Matthew Snape, Professor in Paediatrics and Vaccinology at the University of Oxford, and Chief Investigator on the trial, said:


“This paper summarises data that have been made available to policy makers globally during the pandemic, providing vital information the impact of using short vs long intervals for a range of COVID-19 vaccine schedules. These data are relevant not only to COVID-19 vaccines, but also how future vaccines using mRNA and viral vectored platforms against different diseases may be best deployed.”


Professor Saul Faust, Consultant Paediatrician at University Hospital Southampton and Professor of Paediatric Immunology and Infectious Diseases at the University of Southampton, said:


“I’d like to say a huge thank you to everyone who took part. With your help, we have discovered how we can make the most of our current COVID-19 vaccine supplies.


“This is particularly important for vaccinating those in low to middle income countries. Findings from this study could shape COVID-19 vaccine policy across the world.”


Com-COV is currently looking for 12 to 15 year olds to take part in a study to analyse third dose options for young people.