Johnson & Johnson and AstraZeneca have both been instrumental to the global vaccine effort but rare reports that link their vaccines to blood clots have partly hampered the coronavirus vaccine rollout. Several EU countries have restricted the use of both vaccines while investigations seek to establish the risk. According to a report by Reuters, international drug regulators have said the benefits of using COVID-19 vaccines developed by Johnson & Johnson and AstraZeneca outweigh risks as they investigate reports of extremely rare, but potentially fatal blood clots.
The European Medicines Agency (EMA) said most clots had occurred in the brain and abdomen.
Shedding further light on the nature of the clots, the US Centers for Disease Control (CDC) said the clotting events have been documented in numerous areas of the body, including the femoral vein and artery, internal jugular vein, upper extremity veins and the pulmonary artery.
As of April 20, there had been more than 300 clotting incidents with low platelets reported, out of tens of millions of shots administered.
That included 287 cases of clotting – including CVST and splanchnic vein thrombosis (SVT) which is clotting in veins in the abdomen – linked to the AstraZeneca vaccine.
Europe’s regulator is now reviewing the first report in the region of a death potentially linked to J&J’s vaccine, after a 37-year-old woman in Belgium suffered from a blood clot with low platelets.
More than 1.34 million J&J doses have been administered within the EU.
How have the companies responded?
J&J has said that no clear causal relationship has been established between the vaccine and the clots.
It resumed shipping its one-dose vaccine to Europe and the United States in late April with a warning on its label after a brief pause due to US clotting cases.
AstraZeneca, whose vaccine packaging also includes a warning label required by regulators, has said it is working to understand individual cases and “possible mechanisms that could explain these extremely rare events”.
The regulatory position
The CDC has said it has found a “plausible causal association” between J&J’s shot and clotting after identifying 28 cases of the side-effects among around nine million people who had received J&J’s vaccine.
The US Food and Drug Administration (FDA) has said the vaccine is safe and effective in preventing COVID-19, while issuing guidance to medical professionals on how to respond, should clots emerge.
Europe’s drug regulator has also found a possible link between rare clotting and J&J and AstraZeneca shots, but maintained the benefits of getting vaccinated outweighed the risks.
It has recommended that anyone who developed blood clots with low blood platelets after receiving the first dose should get an alternative shot for the second dose.
The agency has left it up to individual countries to decide how to administer the shots, saying factors may vary including infection rates and whether there are vaccine alternatives to influence local policies.
Britain’s Medicines and Healthcare products Regulatory Agency (MHRA) recommended people under 40 get an alternative vaccine to AstraZeneca’s citing low levels of COVID-19 infection there and the availability of other vaccines.
Are there any plausible explanations for the link?
New research conducted German scientists suggests the mechanisms deployed in specific vaccines could hold the key.
COVID-19 vaccines that employ adenovirus vectors – cold viruses used to deliver vaccine material – send some of their payload into the nucleus of cells.
Some of the instructions for making coronavirus proteins can be misread, potentially triggering blood clot disorders in a small number of recipients, the researchers suggested.