Paediatric trial of AstraZeneca COVID-19 vaccine paused as adult clot link probed

The University of Oxford, AstraZeneca's partner on the COVID-19 vaccine Vaxzevria, said it has suspended a trial testing the inoculation in children and adolescents pending an update from UK regulators about persistent concerns that it may be linked to rare cases of blood clotting. "Whilst there are no safety concerns in the paediatric clinical trial, we await additional information from the MHRA (UK's Medicines and Healthcare products Regulatory Agency) on its review of rare cases of thrombosis/thrombocytopaenia that have been reported in adults, before giving any further vaccinations in the trial," the university said.

The study, which got under way in mid-February, was looking to recruit 300 young people aged six to 17 years, with up to 240 receiving Vaxzevria, while the remainder would be given a control meningitis vaccine. An initial data readout was expected by this summer. Oxford has not disclosed how many participants have received a dose of the vaccine so far. Plans were to test it on children 12 to 17 years old first before moving to the younger age group. The Oxford trial website shows only one site in Southampton is recruiting volunteers, ages six to 11 years old.

The European Medicines Agency (EMA) is currently reviewing rare cases of cerebral venous sinus thrombosis (CVT) among people who have received the AstraZeneca vaccine, and is expected to announce its updated findings on Wednesday or Thursday. Following an initial review last month, the agency said it believes Vaxzevria's benefits at preventing COVID-19 outweigh any potential risks, but it was unable to rule out the possibility conclusively, and so it recommended raising awareness by including a warning on the product. The EMA probe remains ongoing, but earlier on Tuesday, the agency's vaccines head Marco Cavaleri was quoted in an Italian newspaper as saying there was a "clear" link between Vaxzevria and the occurrences of CVT, "but we still have to understand how this [blood clotting] happens."

UK said to be mulling restrictions

The MHRA has said  that as of March 24, there were 30 cases of CVT and eight other thrombosis events with low platelets among 18.1 million people in the UK so far given Vaxzevria, while seven of the cases were fatal. According to a report in the UK, where the vaccine has been authorised since the end of December for use in adults, the MHRA may soon advise people under the age of 30 not to take it.

Johnson & Johnson, Moderna as well as Pfizer and its partner BioNTech are also conducting paediatric trials of their respective coronavirus vaccines, with the latter having already reported positive interim results among 12-to-15-year-olds.

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