The Oxford-led pediatric trial started in mid-February and is aimed at testing the vaccine in more than 200 young people aged 6 to 17 years. An Oxford spokesman said Tuesday that no safety issues have arisen in the trial itself, but broader concerns about rare clotting problems in adults have triggered further regulatory reviews in the U.K. and Europe to investigate any potential link with the vaccine.
Oxford is waiting for more information from the U.K.’s drugs watchdog, the Medicines and Healthcare products Regulatory Agency, before giving any further vaccinations to children or teenagers in the pediatric trial, the spokesman said.
The pause is the latest setback for the Oxford-AstraZeneca shot, which has faced questions about its efficacy and potential side effects even as tens of millions of doses have been administered following safety signoffs in more than 70 countries.
AstraZeneca said last month it plans to ask the U.S. government by mid-April to authorize the vaccine for use there. Europe’s primary medicines watchdog, which has continued to recommend the shot, plans to update the public this week on its review of clotting issues.
The pediatric study, funded by the U.K.’s National Institute for Health Research and AstraZeneca, aims to enroll 300 volunteers in Oxford, London and two other U.K. sites. Of those, more than 200 were expected to receive the vaccine and the rest a placebo, Oxford said. The NIHR referred questions to Oxford. An AstraZeneca spokesman said the company was awaiting the outcomes of the regulatory reviews and declined to comment further.
Oxford hasn’t disclosed how many study participants have received a dose of the vaccine so far. The trial website shows only one site is recruiting volunteers, ages 6 to 11 years old.
The Oxford-AstraZeneca vaccine, a pillar of the U.K.’s mass inoculation drive, is authorized for widespread use in the country among adults over 18.
Globally, vaccine makers are hoping to roll out shots to teenagers and children soon to expand protection beyond adults. Pfizer Inc. and BioNTech SE said last month that their Covid-19 vaccine safely protects children aged 12 to 15. That was based on a study showing the shot 100% effective in protecting against symptomatic disease in more than 2,200 children.
The Oxford-AstraZeneca vaccine was shown to be safe and effective against symptomatic Covid-19 in large-scale human trials in the U.K. and U.S. But some experts say the blood-clotting troubles seen in rollouts are so rare that they might not show up in clinical trials.
The British government said last week that 30 severe blood-clotting cases were reported in the U.K. out of 15.8 million administered doses of the Oxford-AstraZeneca vaccine, according to data as of March 21. Seven of the people died, the regulator has told reporters. The cases included 22 reports of cerebral venous sinus thrombosis, or CVST, and eight reports of other thrombosis events with low platelets. No similar rare-clotting cases were reported in U.K. recipients of the Pfizer-BioNTech vaccine, the MHRA said.
The MHRA has continued to recommend use of the Oxford-AstraZeneca vaccine to all adults over 18 years old, saying the shot’s benefits outweigh its risks.
The regulator said that a “thorough and detailed review is ongoing.” The agency—like its European Union counterpart, the European Medicines Agency—has said there is no proven link between rare, serious blood clots and the vaccine, though a connection also can’t be ruled out. Severe clots occur naturally in the population and can also be caused by Covid-19.
Still, there is growing evidence of a link between the rare, sometimes life-threatening conditions and the vaccine, according to a top EMA official and scientists in Europe who last month said they identified a mechanism that could lead the shot to cause potentially deadly blood clots in rare instances. The scientists, from Norway and Germany, said they also found a possible treatment. Most of the people they studied who were affected were women under age 55.
AstraZeneca has said it is continuing to analyze its database covering tens of millions of vaccinations to understand whether blood clotting is occurring more commonly than would be expected in the general population. It is also working with governments and regulators to address such questions.
Europe’s medicines watchdog said Tuesday that it would update the public this week on its latest findings. The EMA last month said the vaccine was safe and effective despite rare instances of severe clotting, including several deaths, and recommended its continued use. Still, the EMA recommended raising awareness by including a warning with the vaccination and informing the public.
That followed decisions by countries including Italy, France and Germany to suspend the vaccine’s use following reports that people who had received it developed rare blood clots and that some had died, further slowing Europe’s already slow vaccination rollout.
The EMA’s head of vaccines strategy, Marco Cavaleri, told the Italian daily Il Messaggero in an article published Tuesday that the vaccine’s benefits remain greater than its risks, but he said a link between the shot and unusual blood clots with low platelet counts appears likely.
Dr. Cavaleri told the newspaper that preliminary conclusions from the EMA this week are unlikely to recommend age restrictions on the vaccine’s use, as some countries have done. He said that is a decision for individual countries to make based on their vaccine rollout plans, infection rates and the ages of people considered most at risk.
“Of course, it would be preferable for there to be a single position at the European level,” Dr. Cavaleri said. “But…let’s not forget that Covid is hitting various countries differently. In Italy, 500 people are still dying every day [and] in Norway almost nobody is dying. These factors justify different approaches,” he said.
Last week Germany restricted use of the vaccine for people younger than 60 following fresh reports of blood-clotting events among recipients. People under 60 can get the shot only if they request it, and that request must be granted by a doctor, the German government said. Chancellor Angela Merkel told reporters that the government cannot ignore cases of very rare but serious thrombosis.
This story has been published from a wire agency feed without modifications to the text.