A UK study analyzed participants who received a combination of vaccines and concluded that two had the highest negative effects. Fever was the most often reported adverse reaction to these combo vaccinations.
The findings showed that mixing Pfizer and Astrazeneca Covid jabs resulted with more frequent side effects.
In comparison to the typical two doses of either vaccination, providing a single dose of each resulted in a significantly greater rate of mild to moderate symptoms.
The Com-Cov trial, led by Oxford University, enrolled 830 participants aged 50 and over and examined the efficacy of mixed-dose regimens. Overall, both mixed-dose schedules led to a greater incidence of negative events, including fever (34 percent).
Other symptoms included:
- Chills
- Fatigue
- Headache
- Joint pain
- Malaise
- Muscle ache.
“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,” said Matthew Snape, the trial’s chief investigator and associate professor in paediatrics and vaccinology at the University of Oxford.
“It’s just that they’re occurring more frequently,” said professor Snape.
He added: “The best course of action remains getting two doses of the same vaccine.
“Large clinical trials have clearly demonstrated that this strategy reduces the chances of getting COVID-19.
“Your default should be what is proven to work.”
The researchers waited four weeks between doses in the study.
Additionally, the study discovered that the order of vaccination had an effect, with AstraZeneca followed by Pfizer producing the best immune response of the two mixed dosage regimens.
The results indicate that when administered at a four-week interval, both mixed schedules generate an immune response that is greater than the threshold defined by the Oxford-AstraZeneca vaccine’s conventional schedule.
“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,” prof Snape added.
“Reactions often relate to the stimulating of the innate immune response, so that fundamental part of the immune response sends an inflammatory signal.
“Whether or not this will relate to actually improved immune response, we don’t know yet.”
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