Ins and outs of J&J vaccine suspension

THE POTENTIAL side effect is a blood clot in the veins that drain blood from the brain. This is called central venous sinus thrombosis.

In the vaccine-associated cases of this, platelets in blood, which are important for making clots, have been lower than normal.

This same side effect has been seen in the AstraZeneca Covid-19 vaccine that also uses an adenovirus to deliver the coronavirus spike glycoprotein. In the case of the AstraZeneca vaccine, the clotting disorder has been linked to antibodies against platelet factor 4 (PF4) that are apparently induced by the adenovirus backbone of the vaccine. This antibody causes the clotting disorder by activating platelets to clot.

It is important to note that this disorder, called vaccine-induced immune thrombotic thrombocytopenia, is not a problem with the mRNA-based Pfizer and Moderna Covid-19 vaccines.

How many people have experienced this possible reaction?

As of April 13, about one in a million: six cases out of the 6.8 million doses of the J&J vaccine (have been) administered in the US. These six cases all occurred in women of ages 18 to 48, and from six to 13 days after vaccination. That’s about half as likely as getting struck by lightning in a year.

A seventh case was included in the ACIP review on April 14.

The CDC and FDA are recommending that people who have received the J&J vaccine within the past three weeks who develop severe headache, abdominal pain, leg pain or shortness of breath contact their health-care provider.

This type of blood clot is treatable with the use of blood thinners or anti-coagulants.

If a patient has low platelets, however, a doctor would not prescribe the widely used anti-coagulant heparin, but instead another kind of blood thinner. Untreated, these blood clots can be fatal.

What are the CDC and FDA specifically recommending for the J&J vaccine?

Because of this rare occurrence, even though it has not been shown to be due to the vaccine, the CDC and FDA have recommended a pause in use of the J&J vaccine until these cases can be further reviewed.

The CDC convened a meeting of the Advisory Committee on Immunisation Practices on April 14. The ACIP is an independent board of 15 scientific and medical experts selected by the health and human services secretary that advises the CDC on vaccines for children and adults. People with ties to vaccine manufacturers are excluded from the ACIP membership because of potential conflict of interest.

On April 14, ACIP reviewed the available evidence, but did not vote on recommendations because panel members expressed concern that the panel needed more time to evaluate the data and risks. The vaccine has been given to 3.8 million people in the past two weeks. Therefore, not enough time has passed to see whether other people might also experience these serious clots. The panel is expected to meet again within a week to 10 days.

A similar rare problem of blood clotting with low platelets in the cerebral venous sinus and also in the abdominal veins and arteries has been seen in connection with the use of the AstraZeneca Covid-19 vaccine used in Europe. There, 182 cases were reported in 190 million doses – again, roughly 1 in 1 million people vaccinated.

The European Medicines Agency investigated this and concluded that central venous sinus thrombosis with low platelets should be listed as a possible “very rare side effect” of the AstraZeneca vaccine.