On April 13, the Centers for Disease Control and Prevention, as well as the Food and Drug Administration, recommended providers pause on administering the Johnson & Johnson/Janssen COVID-19 vaccine after more than 6.8 million people in the United States received the one-dose vaccine. It comes after six women who received the vaccine experienced blood clots in the brain within two weeks after vaccination.
How does the J&J vaccine work?
It is a viral vector vaccine. This means it uses an inactivated virus (in this case adenovirus) to enter a cell in our body, and then uses the cell’s machinery to create a spike protein on that cell. Next, our immune system recognizes that the protein does not belong there and creates an immune response (antibodies) against it. In the future, when we are exposed to COVID-19, our bodies will quickly recognize that spike protein and fight it off with the antibodies that it already knows how to make.
This adenovirus vector technology is the same technology used in the AstraZeneca vaccine in Europe (not approved or given in the US). There has been a similar link to a rare blood clotting disorder following the AstraZeneca vaccine, prompting the recall of that vaccine as well. There has been a specific mechanism proposed for the rare clotting events after the AstraZeneca vaccine, and we don’t yet know if the same mechanism might be involved with these clotting events found after the Janssen vaccine.
Most cases of blood clots following both vaccines occurred in otherwise healthy, young females.
What to do if you received a J&J vaccine?
Mild flu-like symptoms are expected 1-2 days following the vaccine. However, if you become ill beyond this period up to 3 weeks following the vaccine, specifically if you develop a severe headache, abdominal pain, nausea/vomiting, or visual changes then you should seek medical attention.
Does this mean I should avoid COVID-19 immunization altogether?
Keep in mind that 6 cases out of 6.8 million doses have occurred. The risk of blood clots in patients with COVID is far higher than the very small risk of a blood clot following a COVID-19 vaccine. The blood clots identified after the Johnson & Johnson vaccine are concerning, but seem to be quite rare. This is precisely why we have “Phase 4” of vaccine development which is continually monitoring for serious, unexpected adverse events. Neither the Moderna nor Pfizer vaccines (which are both mRNA vaccines instead of viral vector vaccines) have an association with blood clots so we encourage you to continue to seek one of those options if you are eligible for immunization.
