By Peter Loftus and Jenny Strasburg 

Johnson & Johnson said Friday there wasn't enough evidence to establish that the company's Covid-19 vaccine causes the rare blood-clotting condition that prompted U.S. health officials this week to recommend a pause in its use.

The New England Journal of Medicine published online a letter from three J&J employees involved in vaccine development and epidemiology saying, "At this time, evidence is insufficient to establish a causal relationship between these events" and J&J's vaccine.

U.S. health authorities this week recommended a pause in vaccinations using J&J's single-dose vaccine while they investigated six cases of a rare blood clot, combined with low blood-platelet counts, in women who had received the J&J vaccine. One of the women died.

The pause is expected to remain in place at least until a federal vaccine-advisory committee meets April 23 to review the matter.

After U.S. health officials recommended the pause, J&J said it was aware of the events and working with health authorities investigating them. A J&J executive said at a U.S. vaccine-advisory panel meeting this week that causality hadn't been fully established between the clot events and its vaccine, but the company recognized they could be a potential risk with the vaccine.

Health authorities in several countries have restricted use recently of J&J's vaccine, and a shot from AstraZeneca PLC and the University of Oxford that uses a similar technology, after receiving reports of people getting blood clots following their vaccinations.

The authorities said they were acting out of caution, while they probe the rare adverse events further.

It isn't clear whether the two vaccines caused the rare cases of blood clots and low counts of platelets, which play a role in clotting.

Researchers in Germany and Norway said last month they found the AstraZeneca-Oxford vaccine could trigger an autoimmune reaction causing blood clots. European health authorities said they had found possible links between the events and the AstraZeneca-Oxford vaccine, though the shot's benefits exceed its potential risks.

AstraZeneca has said it agreed with the assessment of European and other health authorities that its vaccine's benefits outweighed its risks. The company hasn't said whether it agreed there was evidence of a link between its vaccine and severe blood clotting.

"The safety of all patients is paramount and we are working with regulators to understand the individual cases, epidemiology and possible mechanisms that could explain these extremely rare events," AstraZeneca said through a spokesman.

The J&J researchers wrote to the medical journal in response to a case report the journal published earlier this week, describing the clotting condition in a 48-year-old woman in Nebraska, which developed two weeks after she received the J&J vaccine. She was critically ill at the time of the case report.

The doctors who wrote the case report about the woman in Nebraska suggested that the rare clotting events, coupled with low platelets, could be related to the type of vaccine technology in the J&J vaccine, known as viral vector.

They noted that similar cases had been seen in recipients of the AstraZeneca's vaccine, which is also a viral-vector vaccine.

The J&J researchers said in their letter the six cases were among more than 7.2 million people vaccinated with J&J's shot. The researchers also said there were differences between the designs of J&J's vaccine and the AstraZeneca-Oxford shot, and therefore the vaccines may have different biologic effects.

"We continue to work closely with experts and regulators to assess the data, and we support the open communication of this information to health care professionals and the public," the J&J researchers said.

The letter was written by Jerald Sadoff, senior adviser with J&J's vaccine division; Kourtney Davis, senior director and head of global epidemiology at J&J's pharmaceutical division; and Macaya Douoguih, head of clinical development and medical affairs with J&J's pharmaceutical unit.

Write to Peter Loftus at peter.loftus@wsj.com and Jenny Strasburg at jenny.strasburg@wsj.com

 

(END) Dow Jones Newswires

April 16, 2021 13:54 ET (17:54 GMT)

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