Mixing COVID-19 vaccines increases an individual’s reactogenicity compared to standard schedules, according to preliminary data from the Com-COV study.
Com-COV, led by the University of Oxford, UK, was launched earlier this year to investigate alternating doses of the Oxford-AstraZeneca vaccine and the Pfizer vaccine, say there are more frequent mild to moderate reactions.
A peer-reviewed research letter in The Lancet today reveals a four-week interval both of the mixed schedules induced more frequent reactions following the second dose than the standard schedules.
Any adverse reactions were short lived and there were no other safety concerns.
The non-inferiority study trial involved 830 volunteers aged 50 and over from eight National Institute for Health Research (NIHR) supported sites in England to evaluate the four different combinations of prime and booster vaccination: a first dose of the Oxford-AstraZeneca vaccine followed by boosting with either the Pfizer vaccine or a further dose of the Oxford-AstraZeneca vaccine, or a first dose of the Pfizer vaccine followed by boosting with either the Oxford-AstraZeneca vaccine or a further dose of the Pfizer vaccine.
In April, the programme was expanded to include the Moderna and Novavax vaccines (Com-Cov2), which was run across nine National Institute for Health Research supported sites by the National Immunisation Schedule Evaluation Consortium (NISEC).
Volunteers would have received either the Oxford-AstraZeneca or Pfizer vaccine, and then randomly allocated to receive either the same vaccine for their second dose or a dose of the COVID-19 vaccines produced by Moderna or Novavax.
Chief investigator Matthew Snape, associate professor in paediatrics and vaccinology at the University of Oxford, said: “Whilst this is a secondary part of what we are trying to explore through these studies, it is important that we inform people about these data, especially as these mixed-doses schedules are being considered in several countries.
“The results from this study suggest that mixed dose schedules could result in an increase in work absences the day after immunisation, and this is important to consider when planning immunisation of healthcare workers.
“Importantly, there are no safety concerns or signals, and this does not tell us if the immune response will be affected. We hope to report these data in the coming months. In the meantime, we have adapted the ongoing study to assess whether early and regular use of paracetamol reduces the frequency of these reactions.”
The study data was recorded in participants aged 50 and above and the researchers say there is a possibility such reactions may be more prevalent in younger age groups.
The study has been classified as an Urgent Public Health study by the NIHR and is being undertaken by the NISEC and the Oxford Vaccine Group, with £7 million funding through the government’s Vaccines Taskforce.
Six new ‘arms’ of the trial each aimed to recruit 175 candidates.
Lancet 13 May 2021
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