Covid-19 vaccine ‘mix and match:’ Benefits of an mRNA second dose


A nationwide cohort study in Sweden has shown ‘mixing and matching’ vaccines is safe, just as the Food and Drug Administration (FDA) has approved a mix and match approach for booster shots in the United States.

Study shows that having an mRNA Covid-19 vaccine dose after an Oxford-AstraZeneca dose offers better protection against infection than two doses of Oxford-AstraZeneca.

Until now, scientists have not known whether ‘mixing and matching’ vaccines offers the same or better protection than receiving two doses of the same vaccine.

One of the most impressive scientific developments to come out of the Covid-19 pandemic was the development of effective vaccines in less than a year.

Some of these vaccines, produced by Pfizer and Moderna, used mRNA vaccine technology for the first time. They have potentially laid the path for further vaccine development.

Others, such as Oxford-AstraZeneca, Johnson & Johnson, and Sputnik, have developed vaccines using more traditional viral vector vaccine technology to protect against the virus.

The discovery of the small risk of thromboembolism from the Oxford-AstraZeneca vaccine, alongside variation in vaccine availability, meant that some people have had to receive a different type of vaccine for their first and second dose.

While evidence existed for an immune response among people who received a traditional vaccine followed by an mRNA vaccine, there was no evidence to show whether mixing the two types of vaccine protected against SARS-CoV-2 infection.

A nationwide cohort study of 721,787 individuals in Sweden has demonstrated that people who have received an Oxford-AstraZeneca vaccine dose followed by a Pfizer or Moderna vaccine dose have more protection against infection than people who received two Oxford-AstraZeneca doses.

The study, published in The Lancet Regional HealthTrusted Source, was the ‘gold standard study’ people had been waiting for, said Professor Monica Gandhi, professor of medicine at the University of California, San Francisco (UCSF), who was not involved in the research.

“I think it should essentially push any region of the world that is using an adenovirus DNA vector [vaccine to say] that that should be the first dose but the second dose, if at all possible worldwide, should be the mRNA vaccine, because this is the gold standard study.”

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