• Quote: ‘Researchers hope that mix-and-match COVID-19 vaccination regimens will trigger stronger, more robust immune responses than will two doses of a single vaccine’

By Andrew Atkinson

Some appointments for the AstraZeneca vaccine have been cancelled by the health authorities for second dose vaccines this month.

I had my appointment for June 30 in Torrevieja cancelled on June 8.

Others have also been notified of unexpected cancellations.

“I had my second AstraZeneca vaccine appointment cancelled and I’m awaiting further details,” said Torrevieja based Peter Deaves.

Angela Crookes said: “I received notification my second vaccination cancelled for June 29 and have no news yet, regarding re-scheduling.”

Heather Brown said: “When I asked at Lo Maribu medical centre I was told they didn’t have any AstraZeneca vaccine available and I’d be called when they had some.”

Some people who had AstraZeneca vaccine as their first dose have been notified that their second vaccine will be Pfizer.

There has been concerns in some quarters about the mixing of vaccine doses.

However a report undertaken states vaccinating people with both the Oxford–AstraZeneca and Pfizer–BioNTech COVID-19 vaccines produces a potent immune response against the virus SARS-CoV-2, researchers conducting a study in Spain found.

Preliminary results from the trial of more than 600 people — announced on 18 May were the first to show the benefits of combining different coronavirus vaccines, published in www.nature.com.

Researchers hope that such mix-and-match COVID-19 vaccination regimens will trigger stronger, more robust immune responses than will two doses of a single vaccine, while simplifying immunization efforts for countries facing fluctuating supplies of the various vaccines.

“It appears that the Pfizer vaccine boosted antibody responses remarkably in one-dose AstraZeneca vaccinees. This is all around wonderful news,” says Zhou Xing, an immunologist at McMaster University in Hamilton, Canada.

Commencing in April, the Spanish CombivacS trial enrolled 663 people who had already received a first dose of the Oxford–AstraZeneca vaccine, which uses a harmless chimpanzee ‘adenovirus’ to deliver instructions for cells to make a SARS-CoV-2 protein.

Two-thirds of participants were randomly picked to receive the mRNA-based vaccine made by Pfizer, based in New York City, and BioNTech, in Mainz, Germany, at least eight weeks after their first dose.

The study was led by the Carlos III Health Institute in Madrid.

The Pfizer–BioNTech booster seemed to jolt the immune systems of the Oxford–AstraZeneca-dosed participants, reported Magdalena Campins, an investigator on the CombivacS study at the Vall d’Hebron University Hospital in Barcelona, Spain.

After this second dose, participants began to produce much higher levels of antibodies than they did before, and these antibodies were able to recognize and inactivate SARS-CoV-2 in laboratory tests. Control participants who did not receive a booster vaccination experienced no change in antibody levels.

That is what researchers hoped for and expected from mixing different vaccines, a strategy known as a heterologous prime and boost, which has been deployed for vaccines against other diseases, such as Ebola. “These responses look promising and show the potential of heterologous prime–boost regimens,” says Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center in Boston, Massachusetts.

Xing says the antibody response to the Pfizer boost seems to be even stronger than the one most people generate after receiving two doses of the Oxford–AstraZeneca vaccine, according to earlier trial data.

Daniel Altmann, an immunologist at Imperial College London said: “A strong immune response to the mix-and-match strategy is entirely predictable from the basic immunology.

“Giving people first and second doses of different vaccines probably makes sense.”

In the Spanish CombivacS trial, mild side effects were common, and similar to those seen in standard COVID-19 vaccine regimens. None was deemed severe.

*Full article can be read at: https://www.nature.com

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