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As J&J pause lifts, investigations continue into cause, risk factors behind rare blood clots

Apr 24, 2021 | 1:54 AM GMT

FDA and CDC have lifted the pause on Johnson & Johnson’s COVID-19 vaccine, but additional work remains ongoing to identify the cause of and risk factors for the rare blood clotting events that triggered the pause to begin with. 

At a press briefing late Friday, Peter Marks, FDA’s Director of the Center for Biologics Evaluation and Research (CBER), said the agency has yet to find associations between cerebral venous sinus thrombosis (CVST) combined with thrombocytopenia and typical risk factors for blood clots such as oral contraceptives or genetic predispositions.

He expects more information to become available in the next couple of weeks. 

“A variety of investigations are either under way or planned to look at whether there are associations, for instance with the immune background, the HLA type, of individuals, etcetera. We don’t know that there’s a connection yet, but because there seemed to be perhaps differences in different populations in the incidents, that’s something that has to be investigated,” said Marks. 

The regulatory lift comes after CDC’s Advisory Committee on Immunization Practices (ACIP) voted 10-4, with one abstention, on Friday to recommend resuming unrestricted use of COVID-19 Vaccine Janssen in adults ages 18 and older.

FDA paused the vaccine’s use on April 13, when it knew of six cases of the rare blood clots in 6.8 million people administered the Johnson & Johnson (NYSE:JNJ) vaccine.

As of April 21, there were 15 confirmed cases of CVST combined with thrombocytopenia reported to FDA and CDC’s Vaccine Adverse Event Reporting System (VAERS), including three deaths, following administration of nearly 8 million doses in the U.S. All 15 cases were observed in women ages 18-59. One case observed during Phase III testing was in a male trial participant. 

J&J has agreed with FDA to modify its healthcare provider and patient fact sheets to note an increased risk of CVST combined with thrombocytopenia. 

CDC had asked ACIP to consider recommending that FDA include a warning statement about clotting events in the EUA. FDA officials believe that by posing the question to ACIP, CDC overstepped its authority, as CDC usually makes decisions about whether and how vaccines will be used, while FDA has authority over approvals, including indications and warnings. 

Last week, EMA added a safety warning to J&J’s vaccine, but stopped short of narrowing the indication to a specific population, and said there are insufficient data to assert that there is a class effect among adenovirus vector vaccines. Though adenovirus vector vaccine Vaxzevria (AZD1222) from AstraZeneca plc (LSE:AZN; NASDAQ:AZN) also is associated with rare blood clots, the two vaccines employ different types of adenovirus vectors and have other differences between them. The AEs have yet to be reported for other adenoviral vector vaccines such as Sputnik V from the Gamaleya Institute.

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