February 28, 2024

A person walks past a sign that reads “The vaccine is our best shot against COVID-19” on the Upper West Side amid the coronavirus pandemic in New York City on March 30, 2021.

Noam Galai | Getty Images

Johnson & Johnson has privately asked Covid-19 vaccine competitors Pfizer and Moderna to participate in a study examining the potential risk of blood clots. The companies refused, however, the Wall Street Journal reported on Friday, citing people familiar with the matter.

Pfizer and Moderna executives said their vaccines were safe and they didn’t see the need to redouble efforts by regulators and companies already addressing the rare blood clot problem, the journal’s report said.

Only AstraZeneca, whose vaccine raised regulatory concerns about blood clots, agreed to join the effort, the Journal said.

CNBC has asked the four companies to comment.

On Tuesday, the Food and Drug Administration and Centers for Disease Control and Prevention advised states to temporarily suspend use of J & J’s vaccine “out of caution” after six women developed a rare but potentially life-threatening bleeding disorder Dead and one left in critical condition.

The women developed a condition known as cerebral venous sinus thrombosis (CVST) within about two weeks of receiving the shot, US health officials told reporters. CVST is a rare form of stroke that occurs when a blood clot forms in the venous sinuses of the brain. It can eventually leak blood into the brain tissue and cause bleeding.

A CDC panel on Wednesday decided to postpone a decision on J & J’s vaccine use while officials investigate the cases.

Read the full Wall Street Journal report here.