Experts at the European Medicines Agency are preparing to present the conclusions of their investigation later on Tuesday into possible links between the Johnson & Johnson coronavirus vaccine and very rare cases of unusual clotting disorders detected in the US.
Last week, J&J halted its European rollout of its one-dose vaccine after the US Food and Drug Administration recommended officials pause its use while the rare blood clot cases are examined. Officials identified six cases of the highly unusual blood clots among nearly 7 million people who were immunized with the shot in the US.
J&J advised European governments to store their doses until the EU drug regulator issued guidance on their use; widespread use of the shot in Europe has not yet started.
The delay was a further blow to vaccination efforts in the European Union, which have been plagued by supply shortages, logistical problems and concerns over unusual blood clots also in a small number of people who received the AstraZeneca COVID-19 vaccine. Experts worry the temporary halt on J&J’s shot could further shake vaccine confidence and complicate worldwide COVID-19 immunization efforts.
Last week, South Africa suspended its use of the vaccine in the wake of the US pause, and countries including Italy, Romania, the Netherlands, Denmark and Croatia put their J&J doses into storage.
The blood clots linked to the J&J vaccine are occurring in unusual parts of the body, such as veins that drain blood from the brain. Those patients also have abnormally low levels of blood platelets, a condition normally linked to bleeding, not clotting.
With the AstraZeneca vaccine, scientists in Norway and Germany have suggested that some people are experiencing an abnormal immune system response, forming antibodies that attack their own platelets.
It’s not yet clear if there might be a similar mechanism with the J&J vaccine. But both the J&J and AstraZeneca vaccines, as well as a Russian COVID-19 vaccine and one from China, are made with the same technology. They train the immune system to recognize the spike protein that coats the coronavirus. To do that, they use a cold virus, called an adenovirus, to carry the spike gene into the body.
Earlier this month, the EU drug regulator said there was a “possible link” between the AstraZeneca shot and rare blood clots but said the benefits of vaccination far outweigh the risks of COVID-19. It noted the risk is less than the blood clot risk that healthy women face from birth control pills.