By Haruna Gimba
Combining doses of the AstraZeneca vaccine with other vaccines may cause more side effects, according to preliminary results from a new study conducted in the United Kingdom.
The Com-Cov study was launched in February to compare the effect of administering a first dose of the vaccine developed by Oxford and drug company AstraZeneca AZN, followed a few weeks later by the vaccine made jointly by drug company Pfizer and its partner BioNTech BNTX, and vice versa.
According to a report published by MarketWatch, the trial, led by the University of Oxford, involved 830 volunteers who are over 50 years old. The participants received four different combinations of the AstraZeneca and Pfizer–BioNTech vaccines.
While the first full results of the study are expected to be published in June, preliminary results, published on Wednesday in a peer-reviewed letter in the medical journal The Lancet, however, revealed that participants receiving a mixed schedule of the vaccines suffered more frequent adverse reactions, such as chills, fatigue, headache, and muscle pain than those on standard non-mixed vaccines.
The study revealed that 34 percent of people who received an AstraZeneca vaccine and later follow up with a Pfizer–BioNTech vaccine were more feverish, compared with 10 percent of those who received two doses of the AstraZeneca vaccine.
The researchers, however, say the adverse reactions were short-lived and had no other safety concerns.
The results will be closely watched by several countries that are considering mixing COVID-19 vaccines in vaccination campaigns, either because of safety concerns about the AstraZeneca vaccines following reports of blood clots in some people or to help shore up supplies.
Associate professor in Paediatrics and Vaccinology at the University of Oxford, and Chief Investigator on the Com-Cov trial, Matthew Snape, said: “Whilst this is a secondary part of what we are trying to explore through these studies, it is important that we inform people about these data, especially as these mixed-doses schedules are being considered in several countries.
“The results from this study suggest that mixed-dose schedules could result in an increase in work absences the day after immunisation, and this is important to consider when planning immunisation of healthcare workers.
“Importantly, there are no safety concerns or signals, and this does not tell us if the immune response will be affected,” Snape said.
The researchers also stated that the side effects of mixing vaccines could be worse for younger people, noting that young people tend to have more active immune responses than participants in the study who were aged 50 and above.
In early February when governments faced the challenges of delivering COVID-19 vaccines to millions of people, a trial involving more than 800 volunteers aged over 50 was inaugurated to see if vaccine combination was advisable.
One group will receive the Pfizer/BioNTech vaccine followed by AstraZeneca’s. Another will be given the inverse, then results will be compared with individuals who received two doses of a single vaccine.
This approach, known as “heterologous boosting” has shown to work in the past.
“Researchers developing some other vaccines, like a better TB vaccine, are looking into heterologous boosting to enhance immunity,” said Peter English, a British public health expert.
“And heterologous boosting is sometimes used in hepatitis B for people who don’t respond well to standard regimes.”
