- J&J asked Pfizer, Moderna, and AstraZeneca to join a study into the potential risk of blood clots, The Wall Street Journal reported.
- Only AstraZeneca agreed, The Journal reported Friday.
- Pfizer and Moderna execs reportedly said their vaccines were safe.
Johnson & Johnson privately contacted other drugmakers producing COVID-19 vaccines to join a study into the potential risk of blood clots, but Pfizer and Moderna refused, The Wall Street Journal reported Friday, citing people familiar with the matter.
J&J contacted Pfizer, Moderna, and AstraZeneca to join the study, but only AstraZeneca agreed, The Journal reported.
Executives at Pfizer and Moderna said their vaccines were safe and that they didn't see the need to duplicate ongoing efforts to look for clotting cases, The Journal reported.
Pfizer said in a statement to Insider on Friday: "Pfizer embraces opportunities for scientific exchange when we can make a meaningful contribution that is not being represented by other groups or regulators. Further, we have and will continue to collaborate with other vaccine makers as appropriate as we all fight against this deadly pandemic."
Insider has contacted Moderna and AstraZeneca for comment.
The US on Tuesday paused the rollout of the J&J vaccine whilst the Centers for Disease Control and Prevention (CDC) and Food and Drug Administration (FDA) investigate whether J&J's vaccine caused blood clots in six people who had received the shot.
All six of those cases involved women between 18 and 48 who developed a rare blood clot in the brain, known as a central venous sinus thrombosis (CVST). The CDC said that 6.8 million Americans had received J&J's vaccine.
"Until that process is complete, we are recommending a pause in the use of this vaccine out of an abundance of caution," the FDA and CDC said in a joint statement.
The J&J also paused its vaccine rollout in Europe and halting vaccinations in trials.
At an American Medical Association webinar on Tuesday, Peter Marks, the director of the FDA's Center for Biologics Evaluation and Research, said that the US had identified just three cases of CVST among the 68 million people who have received a double dose of an mRNA COVID-19 vaccine from either Pfizer or Moderna.
In a Tuesday statement, Moderna said it had carried out its own analysis and found no association between its shot and CVST or other types of clotting.
Anthony Fauci, the US top infectious disease doctor, said Tuesday that he expected the investigation to last "days to weeks".
AstraZeneca's rollout stunted by blood-clot concerns
AstraZeneca's vaccine rollout in Europe was recently stunted over rare clotting concerns as well. The European Medicines Agency last week listed unusual blood clots with low platelets as a very rare side effect of the AstraZeneca vaccine. The agency said that the benefits of the shot in preventing severe COVID-19 outweigh the risks.
Both the AstraZeneca and J&J shots use an inactivated virus to carry the code that tells the body how to make part of the virus, which then triggers the immune response.
As Insider's Aria Bendix has reported, it is not yet clear if the potential links to blood clots are related to this so-called viral-vector technology.
"It's safe to say there's virtually no risk in individuals who received mRNA-based [vaccines], but we don't really have that information yet as far as the viral-vector," Dr. Vivek Cherian, an internal-medicine physician in Baltimore, told Insider.
J&J's vaccine comes in a single dose, while the other three company's vaccines come in two shots.