The break with the Johnson & Johnson Covid 19 vaccine should be days, not weeks, according to CDC and FDA officials.

In a 37-minute online briefing on Tuesday, government health officials said the interruption in administration of the J&J vaccine will give scientists time to investigate what appears to be an autoimmune response that leads to cerebral venous sinus thrombosis, an extremely rare, severe stroke-like reaction.

With more than 6 million doses of the J&J vaccine given to date, there are six known cases of CVST. All occurred in women aged 18 to 48 years. One woman has died and another is in critical condition.

According to Johns Hopkins Medicine, CVST is rare, affecting five in 1 million people. However, the cases of J&J are even rarer as they are accompanied by low platelet counts, according to Dr. Peter Marks, panel member and director of the FDA Center for Evaluation and Research of Biologics.

“At the moment these events seem extremely rare,” said Dr. Marks. “Even so, the safety of Covid-19 vaccines is a top priority for the federal government and we take all post-vaccination events very seriously.”

In the reported cases, the side effect occurred 6 to 13 days after receiving the J&J vaccine. Panel member and assistant chief executive officer of the CDC, Anne Schuchat, MD, realized that the hiatus would worry the people who had received it and tried to allay fears.

“For people who received the vaccine more than a month ago, the risk for them is very low right now,” said Dr. Shuchat. “For people who have recently received the vaccine in the past few weeks, they should be aware that they need to look for symptoms.”

These symptoms include severe headache, stomach pain, leg pain, or shortness of breath. Anyone who experiences any of these symptoms should contact their doctor right away. Dr. Schuchat added that the CDC had not received reports of low platelet counts in more than 190 million people who received either the Pfizer / BioNTech or Moderna vaccines. Both vaccines use a new mRNA technology. The J&J vaccine uses an adenovirus.

The CDC’s Independent Advisory Committee on Immunization Practices was expected to begin reviewing the J&J case data on Wednesday to consider the next step. In the meantime, officials will brief doctors on symptoms and treatment for affected patients.

“We are committed to following the science, ensuring transparency and providing regular updates,” said Dr. Shuchat. “We’ll tell you what we know, when we know, and what you can do to protect yourself. We intend to update you in the coming days. “

While no one is sure what is causing the rare reaction is a leading theory, said Dr. Marks that an immune response activates platelets, which lead to clotting and a stroke-like reaction. Similar cases of blood clotting have been reported in Europe with the AstraZeneca vaccine. In these cases, blood clots formed in the gastrointestinal system.

Robert Calandra is an award-winning journalist and author who has written extensively on health and medicine. His work has been published in national and regional magazines and newspapers.