The pause on the Johnson & Johnson Covid-19 vaccine will allow researchers to investigate a potential link to severe blood clotting events, particularly whether certain populations are more susceptible, National Institutes of Health Director Dr. Francis Collins said Wednesday.
The US Centers for Disease Control and Prevention and FDA recommended a pause on use of Johnson & Johnson’s coronavirus vaccine, following six reported US cases of a rare and severe type of blood clot.
“Many people have heard about blood clots as something that you get in your legs, maybe if nothing is done, they have the risk of spreading to your lungs,” Collins said at a virtual event hosted by the American Association for Cancer Research. “This is a different kind of blood clotting scenario, where there is an activation of the platelets in the body, so that they begin to clot in various places. Most dangerously, this happens in the cerebral venous sinuses inside the skull.”
Collins said that individuals who experience this kind of event have extremely low platelet counts, “because they’ve essentially been consumed.”
Collins noted that the concerns are similar to those raised with the AstraZeneca Covid-19 vaccine, which also uses an adenovirus vector platform.
“Some possibility here that it’s something about the vector that in a very rare individual sets off this cascade,” he said. “We need to figure this out.”
More context: The cases of severe blood clots after vaccination with the J&J vaccine in the US were all among women. Collins noted that the pause will allow researchers to investigate whether particular populations are more susceptible and should perhaps not take the vaccine.
He assured people that the pause will not set back the vaccination effort in the US.
“In fact, the J&J vaccine supply was the smallest of the three and was not going to be particularly critical to get us to the point where everybody would have vaccine access by the end of May, or certainly by June,” Collins said.