Four serious cases of unusual clots accompanied by low blood platelets, including a fatal one, have emerged after vaccination with the J&J shot, the European Medicines Agency said Friday.
One happened during a clinical trial, which, at the time, J&J said it had found no evidence the vaccine was at fault. Three others occurred in the U.S.
The agency said it was investigating these cases and will decide whether regulatory action may be necessary, which usually consists of an update to the product information.
The vaccine was developed by J&J's Janssen Pharmaceutical subsidiary.
J&J said in a statement that it was "aware that thromboembolic events including those with thrombocytopenia have been reported with all COVID-19 vaccines."
"Our close tracking of side effects has revealed a small number of very rare events following vaccination," the company said. "At present, no clear casual relationship has been established between these rare events and the Janssen COVID-19 vaccine."
In March, the European Commission granted conditional marketing authorization to Johnson & Johnson's single-shot vaccine for COVID-19.
The EU rollout isn't expected to start until later this month. The EU is relying on the vaccine to boost its immunization drive after restrictions on use of the AstraZeneca (AZN) - Get Report vaccine in some countries.
The European Medicines Agency said AstraZeneca's COVID-19 vaccine is probably causing deadly blood clots in a small number of vaccinated people.
The EU said it doesn’t yet have enough evidence to approve the Russian Sputnik V vaccine.
Last week, Johnson & Johnson intercepted a batch of drug substance that would have formed part of its coronavirus vaccine production. Reports suggested as many as 15 million doses may have been affected.
The Johnson & Johnson vaccine can be stored and transported at lower temperatures than the competing vaccines from Pfizer (PFE) - Get Report and BioNTech (BNTX) - Get Report, and Moderna (MRNA) - Get Report , which must be kept extremely cold. The competing vaccines also require two shots to J&J's one.
Separately, COVID-19 vaccine sites in North Carolina have stopped administering the Johnson & Johnson vaccine after at least 26 people experienced adverse reactions that included fainting, the Associated Press reported.
In addition, deliveries of the Johnson & Johnson vaccine doses throughout the U.S. are expected to slide by more than 80% next week, according to state officials and federal data, as J&J grapples with manufacturing challenges.
Shares of Johnson & Johnson were off slightly to $162.65 in premarket trading.