J&J says it is 'aware' of blood clots in four Americans who got its vaccine but has seen no proof the shot causes clotting as EU regulators investigate the shot ahead of its rollout

 Johnson & Johnson acknowledged that it is 'aware' of four cases of people developing blood clots after vaccinations with its COVID-19 shot - but that there is no clear evidence that the injections caused clotting. 

EU regulators said on Friday that they are 'investigating' these cases related to J&J's shot, which was approved by the European Medicines Agency (EMA) and is expected to be rolled out later this month. 

To-date, there have been four incidents of blood clots after vaccinations since the J&J rollout began in the U.S. One occurred during its clinical trial, and that person ultimately died of a clotting disorder. 

That's about 0.00008 percent of all J&J vaccines administered in the US, according to a DailyMail.com analysis of Centers for Disease Control and Prevention (CDC) data.

Meanwhile, there have been 41 blood clots following vaccinations with Pfizer's shot logged into the CDC database, known as VAERS. After vaccination with Moderna's shot, 29 people developed clots. 

But far more of each of those vaccines have been given. About 0.00004 percent of people who have received either shot have developed clots. 

In other words, the rates are extraordinarily low for all three vaccines, but about twice as high for Johnson & Johnson's. So why are regulators particularly concerned over J&J's shot? 

That's part of what the EMA's investigation aims to determine. 

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J&J said it is 'aware' of blood clots in four Americans who have had its Covid vaccine (pictured) but has seen no evidence to suggest a causal link. EU health officials are investigating the instances ahead of the rollout of the single dose  

Meanwhile in the U.S., four separate sites in four states have paused vaccinations with J&J's shot after 'adverse events' in at least 37 people. 

The sites were in Colorado and North Carolina - which have now lifted their pauses - and Iowa and Georgia. None of the reactions appear related to clotting issues. 

It also comes after there was a higher rate of blood clots among participants who got Johnson & Johnson's shot in a trial compared to the cate of clots in the placebo group. 

The EMA considers the four cases of blood clots in American recipients of the J&J shot a 'safety signal.' 

Johnson & Johnson's vaccine uses the same technology that AstraZeneca's does. Both use a harmless adenovirus to transport a tiny piece of coronavirus into the body and teach it to make antibodies against COVID-19.    

EMA officials ruled this week that blood clots should be listed as a rare side effect of AstraZeneca's shot for people under 30. 

As detailed in two studies published in the New England Journal of Medicine on Friday, some people develop antibodies that turn 'on' platelets - a clotting component in the blood - leading to blood clots after getting the AstraZeneca vaccine. 

It's a step toward an explanation, but scientists still aren't sure what it is about the vaccine that sets off this chain reaction, or why it happens to only a very few people and not others. 

Naturally, since the 'why' remains unknown, it's still unclear whether this might be the through-line in the EMA's concern over both the AstraZeneca and Johnson & Johnson shots.   

The EMA's safety committee has also been looking at how AstraZeneca's COVID-19 vaccine is associated with very rare cases of unusual blood clots and said it was now reviewing reports of capillary leak syndrome in people given AstraZeneca's vaccine.

J&J said it was aware of the rare reports of blood clots in individuals given its COVID-19 vaccine, and was working with regulators to assess the data and provide relevant information.

'At present, no clear causal relationship has been established between these rare events and the Janssen COVID-19 vaccine,' the company said in an emailed statement.

Of the four serious cases of clotting and low platelets, three occurred in the United States during the rollout of J&J's vaccine from its Janssen unit, the European Medicines Agency (EMA) said. 

That was in addition to one person who died from a clotting disorder reported in J&J's clinical trial.

Nearly five million people in the United States had received J&J's vaccine as of Thursday morning, according to the U.S. Centers for Disease Control and Prevention.

The report from the European Medicines Agency is the first to mention a probe of blood clots associated with the J&J vaccine.

The U.S. Food and Drug Administration (FDA) said it would respond shortly to a request for comment.

It follows a probe of blood clots in the brain reported in people given the AstraZeneca vaccine that have caused some European countries to change their vaccine recommendations.

In its report on Friday, EMA's safety committee said unusual blood clots linked with low blood platelets should be listed as very rare side effects of the AstraZeneca vaccine.

It has also started to investigate reports of capillary leak syndrome - which causes blood vessel swelling and a drop in blood pressure - in five people who received the AstraZeneca vaccine. 

The safety panel said it was not clear whether these were linked with the vaccine. AstraZeneca did not immediately respond to a request for comment.

Ian Douglas, a professor of pharmacoepidemiology at London School of Hygiene & Tropical Medicine, said the reports were part of a normal process in which the EMA's safety committee reviews important safety signals as they arise.

'It's too early to comment on the signal of capillary leak with the AZ vaccine, or clots with the Janssen vaccine, but from what we've seen in the last few weeks, the EMA´s PRAC (Pharmacovigilance Risk Assessment Committee) will doubtless assess all the evidence they have as thoroughly and quickly as possible,' he said.

Some countries in Europe and Asia have restricted the use of AstraZeneca's vaccine, Vaxzevria, in younger people following an update by EU and UK regulators this week that found a link between the events and the shot. Regulators have said the benefits of the vaccine outweigh the risks.

Dr Jesse Goodman, an infectious disease expert at Georgetown University in Washington D.C. and a former chief scientist for the U.S. Food and Drug Administration, said in a briefing on Thursday that he was 'fairly convinced' the brain blood clots were linked with the AstraZeneca vaccine, but said the events are rare and the risk during an active outbreak from COVID 'is much higher.'

J&J's single-dose vaccine has been approved for EU use, but a rollout is yet to begin. It is mainly being used in the United States currently.

The J&J and AstraZeneca shots are two of the four approved COVID-19 vaccinations in Europe.