More frequent side-effects reported mixing Pfizer and Oxford Covid jabs, study suggests | Vaccines and immunisation

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Administering one dose of the Pfizer/BioNTech vaccine followed by one of the Oxford/AstraZeneca vaccine (or vice versa) induces a higher frequency of mild to moderate side-effects compared with standard two doses of either vaccine, initial data from a key UK trial suggests.

The Oxford-led Com-Cov study is exploring the safety and efficacy of mixed-dose schedules given that they are being considered in several countries – including the UK – to fortify vaccine rollout programmes that are dependent on unstable vaccine supplies.

The trial involves 830 participants aged 50 and over, some of whom have underlying conditions. It is testing four combinations: Oxford/AstraZeneca + Oxford/AstraZeneca; Oxford/AstraZeneca + Pfizer/BioNTech; Pfizer/BioNTech + Pfizer/BioNTech; and Pfizer/BioNTech + Oxford/AstraZeneca.

The first tranche of data has come from the group of 463 participants who were given their first and second dose (of any regimen) with a four-week gap. Participants self-reported symptoms in the seven days after the second dose.

Overall, both mixed-dose schedules triggered more side-effects. For instance, feverishness was reported by 34% of patients who got Oxford/AstraZeneca followed by Pfizer/BioNTech; and 41% of those given Pfizer/BioNTech followed by Oxford/AstraZeneca. Meanwhile, only 10% reported feeling feverish in the group who received both Oxford/AstraZeneca doses; and 21% reported the symptom in the group that received two Pfizer/BioNTech doses.

Similar differences were observed for chills, fatigue, headache, joint pain, malaise, and muscle ache. Overall, any adverse reactions that cropped up were short-lived and there were no other safety concerns, according to data published in the form of a letter in the journal the Lancet.

“These are the type of reactions we do expect with vaccines … and they are more or less the same types of reactions that you’re seeing with the standard schedules. It’s just that they’re occurring more frequently,” said Matthew Snape, the trial’s chief investigator and associate professor in paediatrics and vaccinology at the University of Oxford.

Although trial participants were aged 50 and above, real-world data suggests that younger age groups tend to have stronger reactions to vaccines, he noted. “We would expect that this signal … of higher reactions in the mixed schedules, would still come through, and [in] younger age groups there might be even more reactions.”

What this data suggests is that immunising a ward full of nurses on the same day with a mixed schedule may not be ideal because it might trigger higher rates of absenteeism the next day, he said. “In those countries that are starting to think about using these schedules … they may need to prepare for higher rates of absenteeism.

“Reactions often relate to the stimulating of the innate immune response, so … that fundamental part of the immune response that sends an inflammatory signal – whether or not this will relate to actually improved immune response, we don’t know yet,” Snape said.

Data on the efficacy of these mixed-schedule regimens in inducing an immune response is expected in the coming weeks. Trial investigators are also evaluating the impact of dosing participants 12 weeks apart.

Another study called Com-Cov2 will assess the impact of participants receiving either the Oxford/AstraZeneca or Pfizer/BioNTech vaccine, and then either getting the Moderna or Novavax vaccine for their second dose.

Hafta Ichi
Source: The Guardian
Keyword: More frequent side-effects reported mixing Pfizer and Oxford Covid jabs, study suggests | Vaccines and immunisation

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