There is not a lot of data to go on, But during the clinical trials there were more thrmobembolic events in the vaccine group compared to placebo, as well as 3 or 4 arterial clots in the vaccine group but not the placebo group.
The European Medicines Agency said Friday that its Pharmacovigilance Risk Assessment Committee (PRAC) has started a review of thromboembolic events following immunisation with Johnson & Johnson’s COVID-19 vaccine Ad26.COV2.S. Although the single-dose vaccine was authorised in Europe last month, rollout in the region is only expected to start in the next few weeks.
According to the EMA, four serious cases of unusual blood clots with low blood platelets have been reported post-vaccination with Johnson & Johnson’s vaccine. The regulator noted that one case occurred in a clinical trial and three were reported during vaccine rollout in the US, where it was granted an emergency-use authorisation in late February. One of the cases proved fatal.
The latest safety signal comes in the wake of an EMA review suggesting a “possible link” between AstraZeneca’s COVID-19 vaccine Vaxzevria and “very rare” blood clots, often cerebral venous sinus thrombosis, that occur concurrently with thrombocytopenia, and that have so far mostly been seen in people under 60 years of age. However, the agency continues to endorse the vaccine, saying its benefits outweigh any potential risks, but some countries have nevertheless restricted its use to older people.
FDA staff flagged blood clotting events
Like Vaxzevria, Johnson & Johnson’s product also uses an adenoviral vector. In the lead-up to US authorisation of Ad26.COV2.S, FDA staff briefing documents highlighted some cases of thromboembolic events, including deep vein thrombosis and pulmonary embolism, that were numerically slightly more common among vaccine recipients than for placebo in the pivotal Phase III ENSEMBLE trial. The agency considered these as being “of clinical interest,” but otherwise found “no specific safety concerns.”
The ENSEMBLE study was paused last October after an “unexplained illness” in one of the participants, but resumed a short time later. A review by the company turned up “no clear cause” for the illness, although a report citing two sources said the volunteer in question had suffered a stroke, which an independent committee concluded was not related to the vaccine.
Second possible side effect for AstraZeneca’s vaccine
Meanwhile, the EMA also said Friday that PRAC is looking into five cases of capillary leak syndrome reported in its EudraVigilance database that have occurred in people administered Vaxzevria. “At this stage, it is not yet clear whether there is a causal association between vaccination and the reports of capillary leak syndrome,” the agency noted, adding that “PRAC will evaluate all the available data to decide if a causal relationship is confirmed or not.”