The US, South Africa and European Union have temporarily stopped the immunisation using Johnson & Johnson (J&J)’s Covid-19 vaccine over cases of rare blood clots.

The cases presented a type of blood clot called cerebral venous sinus thrombosis (CVST), observed in combination with low levels of blood platelets (thrombocytopenia).

All six cases of blood clots occurred among women, aged between 18 and 48, and symptoms occurred six to 13 days after receiving the vaccine.

The United States Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) jointly stated that they are reviewing data comprising six cases of a rare and severe type of blood clot reported in the US after receiving the J&J vaccine.

CDC and FDA said that treating the specific type of blood clot that occurred, in this case, is different from the normal treatment using anticoagulant drug heparin, as its administration may be dangerous.

They stated that it will organise a meeting of the Advisory Committee on Immunization Practices (ACIP) to further review the cases and determine their potential significance.

CDC and FDA, in their statement, said: “Until that process is complete, we are recommending a pause in the use of the J&J vaccine out of an abundance of caution.

“This is important, in part, to ensure that the health care provider community is aware of the potential for these adverse events and can plan for proper recognition and management due to the unique treatment required with this type of blood clot.”

CDC and FDA suggested people developing severe headache, abdominal pain, leg pain, or shortness of breath after receiving the vaccine, to contact their health care provider.

Also, they urged the health care providers to report the previously mentioned adverse events to the Vaccine Adverse Event Reporting System.

J&J’s pharmaceutical business Janssen has developed the vaccine, which showed effectiveness in preventing Covid-19 infection, in clinical trials.

Previously called Ad26.COV2.S, the vaccine is administered as a single dose and can be stored at normal refrigerator temperatures, facilitating easy distribution.

EC authorised J&J’s Covid-19 vaccine to prevent the Covid-19 in people aged 18 years and older, in all 27 EU member states, along with Norway, Iceland and Liechtenstein.

Also, it was previously granted Emergency Use Authorisation (EUA) from the FDA, and authorised in Canada, under an interim order.

In October last year, the company temporarily paused the further dosing of its Covid-19 vaccine candidate in clinical trials, over an unexplained illness in a study participant.