Since alternating doses of the AstraZeneca and Pfizer Covid vaccines, adults are more likely to experience mild to severe side effects, according to a survey. When separate vaccine doses were mixed, chills, headaches, and muscle pain were registered more often. Any negative responses were brief, and there were no other safety issues. Prof Matthew Snape of the Oxford Vaccine Group said, "It's a very intriguing discovery and not what we were necessarily planning."
The Com-Cov research began in February with the aim of determining if a separate vaccine for the second dose will have longer-lasting immunity, improved defense against new strains, or merely encourage clinics to exchange vaccines if stocks were disrupted.
In the wake of controversy about imports of the Oxford-AstraZeneca vaccine and fears over unusual blood clots, the Canadian provinces of Ontario and Quebec have both stated that they plan to combine vaccines in the immediate future.
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The research, which is led by the University of Oxford, has enlisted the help of 830 volunteers over the age of 50.
The first complete reports are scheduled to be released in June.
One in ten volunteers who received two AstraZeneca jabs four weeks apart indicated feverishness, but the proportion increased to about 34% if they received one AstraZeneca and one Pfizer jab in any order.
Prof Snape, the trial's chief investigator, said, "The same actual distinctions applied for other symptoms such as chills, nausea, fever, malaise, and muscle ache."
"One thing it tells us is that you wouldn't like to vaccinate a ward full of nurses on the same day [with combined doses of multiple vaccines], so the following day you may get more absenteeism."
However, preliminary findings have now been presented in a review letter in the Lancet medical journal.