Johnson & Johnson (J&J) and AstraZeneca are looking into modifying their Covid-19 vaccines to reduce the risk of rare but serious blood clots, sources told the Wall Street Journal.

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Background

In April, CDC and FDA recommended a pause in the use of J&J's single-dose Covid-19 vaccine after six people—out of more than 6.8 million people who had received the vaccine at the time— developed a rare and severe type of blood clot called cerebral venous sinus thrombosis (CVST).

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The condition typically involves severe headaches, abdominal pain, leg pain, or shortness of breath, with symptoms most often occurring around six days after vaccination. It can be fatal if it leads to bleeding in the brain.

On April 23, CDC's advisory panel voted to resume use of J&J's vaccine and to add a warning label about the risk of CVST in young women that says the "chance of having this occur is remote."

Meanwhile, in March, several countries in Europe paused the use of AstraZeneca's vaccine—which was developed with the University of Oxford and is not authorized for use in the United States—due to reports of blood clots associated with that shot.

For both shots, instances of CVST are rare, the Journal reports. According to data from the United Kingdom and Europe, the risk of clotting following AstraZeneca's shot are around one to two per 100,000 vaccinations. Meanwhile, the risk of clotting following J&J's shot are around 0.3 per 100,000 doses, according to U.S. data.

J&J, AstraZeneca, Oxford research the possibility of modifying vaccines

Sources told the Journal that J&J, AstraZeneca, and Oxford are initiating early-stage research into whether altering their vaccines could limit or eradicate the risk of developing blood clots.

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To identify what might be spurring the blood clot issue, researchers first need to understand whether the clots are caused by an ingredient in the vaccine, the purification process, or a mechanical aspect of how the shot works, the Journal reports.

Regarding AstraZeneca's vaccine, Sarah Gilbert, a vaccinologist at Oxford and co-inventor of the vaccine, said AstraZeneca and the university are looking into potentially modifying the vaccine's delivery mechanism. She did not predict when any modified vaccine would be ready, but sources told the Journal that researchers hope the underlying issue could be identified—and the vaccine re-engineered—by 2022.

"Progress is being rapidly pursued by the companies, and I think their desire to alter the vector or the vaccine is moving in parallel to explaining" the blood clots, Mortimer Poncz, a pediatric-hematology division chief at the Children's Hospital of Philadelphia, said.

A spokesperson for J&J said the company supports "continued research and analysis as we work with medical experts and global health authorities."

AstraZeneca said it is "actively working with the regulators and scientific community to understand these extremely rare blood-clotting events, including information to drive early diagnosis and intervention, and appropriate treatment." (Strasburg/Olson, Wall Street Journal, 7/13; Lonas, The Hill, 7/13)