Mixing different Covid-19 vaccines appears to give protection against coronavirus.
Thailand became the most recent country to announce a plan that will mix different vaccines, adding to the list of countries that have begun offering mix-and-match vaccinations.
Gloria Taliani, professor of infectious disease at the Sapienza University of Rome, told Al Jazeera that mixing is not a new concept when treating diseases.
"We've used different vaccines [when we treated] other diseases and we don't care if the second dose is a different vaccine compared to the first one, or if the boosting dose is a different one," Taliani said.
Taliani added that while there may be some concerns because this is the first time mRNA vaccines have been used to protect against infectious diseases, there are no scientific reasons to believe that mixing could be harmful.
"There is no biological reason why vaccines that use a different stimulus to the immune system could be harmful to any person," she said.
The University of Oxford's Com-COV trial, which included more than 800 volunteers, looked into the efficacy of two doses of AstraZeneca, Pfizer, or one followed by the other.
Mixed schedules combining the Pfizer vaccine and the AstraZeneca shot produced a high immune response against the virus, according to the results.
The results of the study suggest that the order of the vaccines made a difference, with AstraZeneca being followed by Pfizer "inducing higher antibodies and T-cell responses than Pfizer followed by AstraZeneca."
T-cells promote antibody production and aid in the fight against virus-infected cells. The research also revealed that two doses of Pfizer resulted in the highest degree of antibodies.
Meanwhile, the World Health Organization's chief scientist, Soumya Swaminathan, has urged individuals against mixing vaccinations and said that decisions should be left to health agencies.
"Individuals should not decide for themselves, public health agencies can, based on available data," Swaminathan said in a tweet. "Data from mix and match studies of different vaccines are awaited - immunogenicity and safety both need to be evaluated."