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Covid-19 vaccine mix linked to more side effects, first UK data shows

But the side effects after the mix-and-match vaccinations were short lived and there were no other safety concerns, the researchers reported in the Lancet Medical Journal.

“These are the types of reactions you would expect with the vaccine,” said Dr Matthew Snape, associate professor of pediatrics and vaccinology at the University of Oxford and chief investigator of the trial, during a briefing.

“These are more or less the same types of reactions you see with standard schedules. It’s just that they happen more frequently, and we see the two most common in both mild and moderate symptoms – but they do. resolved quickly, ”Snape said.

Overall, “it’s a really intriguing find,” he said, “and it’s not necessarily something we expected – to see such a consistent signal.”

This is something to watch out for when giving mixed doses, the researchers said.

“One of the things he tells us is that, for example, you wouldn’t want to vaccinate a room full of nurses on the same day with a mixed schedule,” Snape says. “Because you can have higher absenteeism rates the next day.”

The mix-and-match trial

The new research included 830 volunteers aged 50 and over who were randomly assigned to four different vaccination schedules involving the Oxford / AstraZeneca and Pfizer / BioNTech vaccines, with the first and second doses given 28 days apart.

They either received the AstraZeneca vaccine in two doses; AstraZeneca as the first dose and Pfizer as the second dose; the Pfizer vaccine in two doses; or the Pfizer vaccine as the first dose and AstraZeneca as the second dose.

Researchers found that people who received different vaccines had more side effects after the second dose, with fever reported by 34% of those who received the AstraZeneca vaccine first and the Pfizer vaccine second, compared with 10% of those who received the AstraZeneca vaccine first and the Pfizer vaccine second. those who received the AstraZeneca vaccine for both doses. .

Fever was reported by 41% of people who received Pfizer vaccine first and AstraZeneca vaccine second, compared with 21% of volunteers who received Pfizer vaccine for both doses.

“Similar increases were seen for chills, fatigue, headache, joint pain, discomfort, and muscle pain,” the researchers wrote. They noted that people could take acetaminophen – sold under brand names such as Tylenol – to lessen side effects.

There was no hospitalization due to the symptoms and most of the increased reactions were seen within 48 hours of vaccination, the researchers found. They noted that they had not seen any evidence of a rare blood clotting syndrome associated with the AstraZeneca and Johnson & Johnson vaccines in any of the volunteers within a week of the second dose.

Covid-19 vaccine mix linked to more side effects, first UK data shows
The researchers also noted that their results are based on initial data and that there are currently ongoing studies testing the mixed administration of vaccines made by Moderna and Novavax.

More research is also needed to assess immune responses across different types of schedules, and whether increased side effects suggest that schedules using different types of vaccine elicit strong immune responses.

“We believe the reactions are often related to the stimulation of the innate immune response,” Snape said. “We don’t know yet whether or not this will relate to an enhanced immune response. We will find out about these results in a few weeks.”

In search of a “ better insight ”

The United States Centers for Disease Control and Prevention and the World Health Organization do not currently recommend swapping coronavirus vaccines – but the CDC noted in January that its guidelines may be updated as and when as new information and new types of vaccines become available.
There may be benefits to having more flexible vaccination schedules using different types of vaccines as the first and second doses, Dr Jonathan Van-Tam, deputy medical director for England, said in a statement in February when the news research has started.

“Given the inevitable challenges of immunizing large numbers of the population against COVID-19 and the potential constraints of global supply, there are definite advantages to having data that could support a more flexible immunization schedule. , if necessary and if approved by the drug regulator, ”Van -Tam said at the time.

“It is also possible that by combining vaccines, the immune response could be enhanced by giving even higher levels of antibodies that last longer; unless it is evaluated in a clinical trial, we will not know everything. just not, ”he said. “This study will give us better insight into how we can use vaccines to stay on top of this nasty disease.”


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