The road to a covid vaccine will not be a walk. British pharmaceutical AstraZeneca has interrupted clinical trials of its prototype, one of the most advanced in the world, after detecting “a potentially unexplained disease” in one of the volunteers who received the injection, according to a company spokesperson to the health information website Stat News . The experimental vaccine, developed by the University of Oxford together with AstraZeneca, was theoretically the first to be administered in Spain. The European Commission has an agreement with the multinational to buy 300 million doses and the Minister of Health, Salvador Illa, affirmed on August 28 that the first would arrive at the end of December “if everything goes well and security has been guaranteed.”

A spokeswoman for AstraZeneca in Spain assures that the suspension is “a routine action that is carried out, while investigating what happened, whenever a potentially unexplained disease is observed” in one of the trials. “We are working to accelerate the review of this single case in order to minimize any potential impact on clinical study times,” he adds.

AstraZeneca and Oxford are conducting final trials of their experimental vaccine in the UK, Brazil and South Africa and had also started recruiting volunteers in the US, to an expected total of 50,000 participants worldwide. The affected person received a dose in the British trial and has transverse myelitis, according to The New York Times . This neurological disorder is rare – barely 300 cases are detected a year in the UK – and is caused by inflammation of the spinal cord. Dozens of cases have been described in the scientific literature vaccine-linked transverse myelitis, such as hepatitis B or combined mumps, measles, and rubella. The disorder is also associated with viral infections and other causes, so it is not clear that the new case is related to the AstraZeneca injection.

Oxford’s experimental vaccine is made from a weakened version of an adenovirus from the common cold of chimpanzees . The virus is modified with genetic information from the new coronavirus to train the immune system of the vaccinated person without the risk of suffering from covid. The scientist Vicente Larraga, from the Margarita Salas Biological Research Center (CSIC), in Madrid, points out that the appearance of disorders such as transverse myelitis is “relatively normal” “in general with vaccines that use modified viruses as vehicles”. Larraga, father of a vaccine against leishmaniasis in dogs and of a candidate against covid, recalls the difficult road ahead for experimental vaccines: “Of the molecules that begin a preclinical phase [tests in cells and in animals] only one in 10,000 reaches phase IV.

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