First Moderna, then Pfizer? Belgium studies if first and second shot can be different

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Credit: Belga

Four research centres in Belgium are launching a study to find out whether the coronavirus vaccines approved by the European Medicines Agency (EMA) and the country's authorities can be used in a "more flexible way."

Specifically, they want to examine the consequences of getting two shots with two different vaccines: the first with AstraZeneca and the second with Pfizer/BioNTech, for example.

"Everyone knows by now that vaccine deliveries are a very delicate process," said vaccinologist Pierre Van Damme (UAntwerp) in a press release. "Many factors can lead to major delays in vaccination campaigns."

Administering the second shot with a different vaccine, however, could speed up the vaccination campaign, something which four study centres - led by the UAntwerp - are now looking into, in a large-scale study 'IMCOVAS'.

"The vaccines from Pfizer/BioNTech, AstraZeneca and Moderna will be administered during the study according to a different schedule or dosage than is currently prescribed in the information leaflet," said principal investigator Katie Steenackers (UAntwerp).

Participants in the study, aged between 18 and 55, will be assigned to one of 12 different groups, each with its own schedule. "Some participants will receive the first shot with AstraZeneca and a few weeks later a second shot with Pfizer."

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"The large-scale study will provide important information about the safety and immune response of other schedules and/or dosages," Steenackers said. "If the immune response for one of the groups turns out to be lower than expected, the study participants will still receive a standard vaccination schedule."

In France, such a "vaccine switch" is already happening, as people under 56 years old who had already received the first dose of AstraZeneca’s vaccine in early April, are receiving a dose of the Moderna or Pfizer/BioNTech vaccine for their second shot.

According to the World Health Organisation (WHO), however, "there is currently not enough data available yet" to make any reliable statements about whether people can safely get the first dose from one vaccine and a second dose from a different vaccine.

Additionally, scientists are also looking at other options to make vaccination as quick as possible, such as a more flexible schedule to administer vaccines at a lower dose, or at a different interval.

The insights that will come from this study are crucial to accelerate vaccination campaigns across the world, according to the researchers.

"In the West, vaccination campaigns are now running smoothly, but we still have a long way to go globally," Van Damme added. "To really stop the virus, we need success everywhere."

The Centre for the Evaluation of Vaccination (UAntwerp), the Institute of Tropical Medicine, the Centre for Vaccinology (UZ Gent) and Hôpital Erasme (Université Libre de Bruxelles - ULB) are looking for volunteers aged between 18 and 55 for the study.

It will take 12 months, during which volunteers will have to make six visits, and will receive a compensation of €60 per visit.

More information about the study, as well as instructions to register as a volunteer, can be found here.

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