What Happens When You Mix 2 COVID-19 Vaccines, Researchers Find in a Study

In preliminary results from a study, it has been found that mixing doses of two leading COVID-19 vaccines increases the side effects of the patients like fatigue and headaches. The study is still yet to show the efficacy of the mixture of two vaccines against the COVID-19 virus. 

Researchers from the University of Oxford stated in The Lancet medical journal that people who received the first dose of AstraZeneca Plc's vaccine followed by a dose of Pfizer Inc.'s vaccine four weeks later experienced more short-term side effects, the majority of which were mild. That was also valid when the shots were switched in order.

As many low and middle-income countries struggle to find out how to deal with vaccine shortages, researchers and public health authorities are looking at tactics like combining two separate shots. It would be easier for governments to maintain their stockpiles if they could be certain that mismatched shots are both secure and reliable. It would also provide more insight into a mixture that is already used in certain countries. 

People who received the first dose of the AstraZeneca vaccine before the government limited it to older patients in France, for example, are being given the Pfizer and BioNTech SE vaccine as a second injection. 

"It's a really intriguing finding and not something that we were necessarily expecting," said Matthew Snape, an Oxford pediatrics and vaccinology professor who's the leader of the trial. "Whether or not this will relate to an improved immune response, we don't know yet; we'll be finding out those results in a few weeks' time." 

On a conference call, he said the study found no safety concerns and that the stronger side effects faded after a few days. According to Snape, the findings indicate that mixed dose schedules can result in an increase in work absences the day after immunization. 

"You wouldn't want to immunize a ward full of nurses with a mixed schedule on the same day," he said. 

About 10% of participants who got mixed doses reported severe fatigue as compared to about 3% of those administered with a single type of vaccine, the research showed. 

The study's participants are all over the age of 50. According to Snape, the reactions maybe even more powerful in younger patients. 

While not every vaccine works when mixed, the researchers are of the view that combining two vaccines share the same target like the virus's spike protein can be safely administered to COVID-19 patients. 

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