British trials are studying a “mixture” of vaccines

British trials are studying a “mixture” of vaccines

A trial in the UK is trying to see if giving different vaccines in the first and second doses can be effective in preventing coronavirus. Currently, in both the UK and Portugal, health authorities maintain that vaccination should not be combined.

The aim of the trial is to study the possibility of giving greater flexibility in vaccination, to help in the event of a possible unexpected interruption in deliveries, but also to see if there is any “combination” that could provide better protection.

This study received an investment of £7 million from the government (about €8 million) and is expected to include more than 800 volunteers over the age of 50 in England.

Some volunteers will receive the Oxford/AstraZeneca vaccine, followed by the Pfizer/BioNTech vaccine, while others will do the opposite, always four or 12 weeks apart.

The BBC says it is possible to add new vaccines to that study as they have been approved by regulators. Another goal of the research is to understand the impact of immunization on novel variants of the COVID-19 virus.


In the UK, official guidance from the Committee on Immunization and Immunization to date states that vaccination should not be combined. Anyone who has received the Pfizer/BioNTech or Oxford/AstraZeneca vaccine should receive the same immunization for the second dose.

However, it states, in very rare cases, the possibility of using a different vaccine: when only one immunization is available or when it is not known which vaccine was given in the first dose.

In Portugal, at the moment, a ‘mix’ of different doses is not expected in the vaccination schedule. In the standard published by the Directorate General of Health, at the end of January, the first and second doses are expected to be of the same brand.

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“For vaccines with a two-dose schedule, the second should be scheduled after the first dose is given. Scheduling the second dose should ensure that the vaccine used is of the same brand,” the document states.

To date, the European Medicines Agency has approved the Pfizer/BioNTech, Moderna and AstraZeneca vaccines, immunizations that are already or will be available in Portugal. All are multi-dose vaccines.

Possible advantages

From a scientific point of view, there is good reason to believe that this new blending approach could be beneficial. In the fight against Ebola, for example, there are immunization programs that provide different vaccines, in order to provide greater protection.

Nadim Al-Zahawi, the minister responsible for the vaccination process in the UK, points out that mixing doses are common in previous vaccines, particularly in vaccinations against hepatitis, polio, measles and rubella.

However, the British government representative to vaccination stresses that there will be no change in the approach currently taken in the UK, at least until the summer.

The ‘Com-Cov’ trial, conducted by the National Consortium for the Evaluation of Immunization Schedule, is led by Professor Matthew Snape, from the University of Oxford, and is expected to last 13 months, and some conclusions may be reached by June.

In an interview with the BBC, Snape said animal studies had already been done, which showed “a better antibody response” when there is a mixed vaccination schedule.

“It will be interesting to see if different vaccination methods can really lead to an improved immune response, or at least to a response as good as vaccination doses of the same brand,” he added.

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