According to the European Medicines Agency (EMA), the vaccines from AstraZeneca and Janssen cause severe thrombosis in combination with a shortage of platelets in very rare cases.

How common is this side effect?

And what about Moderna and Pfizer?

Severe thrombosis in combination with a platelet deficiency is an extremely rare side effect of the Janssen vaccine.

The EMA announced this on Tuesday.

The AstraZeneca vaccine also has this side effect.

The EMA came to this conclusion after studying eight reports of this disease from the United States.

In the United States, up to April 13, when the country temporarily stopped using the AstraZeneca vaccine, more than seven million people received the Janssen vaccine.

The number of cases on which the EMA relies at Janssen is small.

Sabine Straus, head of the European Pharmacovigilance Committee PRAC, explained during the EMA press conference that researchers are nevertheless convinced that there is a link between the Janssen vaccine and this clinical picture.

This is partly because the reported cases are remarkably similar to the cases after vaccination with AstraZeneca, which have already been investigated by the EMA.

Severe thrombosis in combination with a lack of platelets normally occurs, in the absence of corona vaccines, also in extremely rare cases.

After vaccination with Janssen, this clinical picture occurred more often than is normally expected, according to the EMA.

See also: Why people in their 60s get the AstraZeneca vaccine and younger people don't

On April 4, there were 142 cases of severe thrombosis associated with platelet deficiency in Europe after an AstraZeneca injection.

This is also more than is normally expected, according to the EMA.

In total, more than 16 million AstraZeneca injections were counted in the European Union, Norway, Iceland and Liechtenstein.

This means that approximately nine cases of severe thrombosis associated with platelet deficiency have been reported per million AstraZeneca vaccinations.

Janssen has reported about one case of this syndrome per million injections.

The EMA does not know whether the risk with the Janssen vaccine is really lower than with the AstraZeneca vaccine.

Straus said the side effect is seen in Janssen for up to three weeks after the vaccination. The vaccination with Janssen was stopped a week ago in the US. Some of the seven million vaccinated have only just received the vaccine. In that part, the side effect may develop later. It is therefore not clear how often this side effect now occurs after vaccination with Janssen.

There is no evidence that Moderna or Pfizer cause the same side effect.

According to the EMA, 25 cases of thrombosis in combination with platelet deficiency have been reported worldwide after vaccination with the Pfizer vaccine.

In Europe alone, at least 59 million people have had the Pfizer vaccine.

Moderna has five known cases worldwide.

According to Straus, the number of reported cases is actually lower than normally expected.

It is still unclear whether women are more at risk.

However, with both the Janssen vaccine and the AstraZeneca vaccine, the side effect has mainly been seen in women under the age of 60 years.

It is also unclear whether taking the pill or previous thrombosis increases the risk of this side effect.

The reason that the vaccines from AstraZeneca and Janssen in very rare cases cause severe thrombosis in combination with a shortage of platelets is also not entirely clear.

The EMA suspects that the side effect is caused by a wrong reaction of the immune system after vaccination.

However, it is unclear what exactly is the cause of this in the vaccine.

We therefore do not know whether corona vaccines using the same technique as Janssen and AstraZeneca also have this problem.

The Russian Sputnik V vaccine, for example, also uses this technique.

This vaccine is not currently approved for use within the EU.

See also: This is the technology behind the AstraZeneca and Janssen vaccines