Johnson & Johnson COVID Vaccine Recipients Almost 4X as Likely to Get Blood Clots: Study

A new study conducted in one county in Minnesota has found an increased likelihood that citizens who received the Johnson & Johnson's COVID-19 vaccine were more likely to develop blood clots.

The study by the Mayo Clinic found that recipients of the Johnson & Johnson vaccine, officially designated "Janssen," in Olmsted County, Minnesota, were about 3.7 times more likely to develop a certain variety of cerebral blood clots. Case numbers taken from February 28 to May 7, 2021, were compared to pre-pandemic levels of the blood clots from January 1, 2001, through December 31, 2015.

Census data from 2020 showed that 162,847 people live in Olmsted County.

Previous studies on this issue, the Mayo Clinic study notes, have yielded inconclusive results. Despite the concerning data, it was noted that the number of recipients to develop blood clots was still statistically rare and "considered in the context of the effectiveness of the vaccine in preventing COVID-19."

johnson and johnson vaccine
A new study showed that those who took the Johnson & Johnson COVID vaccine in one Minnesota county were more likely to develop blood clots. Above, pharmacist Antoun Houranieh holds a vial of the Johnson & Johnson Covid-19 Janssen Vaccine at the U.S. Department of Veterans Affairs' VA Boston Healthcare System's Jamaica Plain Medical Center in Boston, Massachusetts, on March 4, 2021. Joseph Prezioso/AFP via Getty Images

The study noted that the risk of developing the blood clots was found to be noticeably higher in women. Female recipients of the Johnson & Johnson vaccine observed in the study were around 5.1 times more likely to have the side effect compared to pre-pandemic numbers. Out of every demographic defined for the study, the risk was found to be the highest in women aged 40-49, followed by women aged 30-39.

It was further stressed, however, that "the absolute [side effect] risk was still low."

"It was surprising that it is predominantly women (especially 30- to 49-year-old women) who are at a higher risk for [cerebral venous sinus thrombosis (CVST)] in the first 15 days after the administration of Johnson & Johnson COVID-19 vaccine," Dr. Aneel A. Ashrani, leader of the study, told Healio.

"We do not have a good explanation for it but speculate that they may have additional/concomitant CVST risk factors, (eg, oral contraceptive pill use) or may have a predisposition to autoantibody production that may have led to vaccine-associated thrombocytopenia with thrombosis," he said.

In April, the rollout of the Johnson & Johnson vaccine was paused after six cases of CVST were reported among recipients. Though it was a small number of cases, top health agencies advocated for the pause while the situation was assessed.

The issue was also observed in the AstraZeneca vaccine. A handful of patients, including BBC presenter Lisa Shaw and British fashion model Stephanie DuBois, died from blood clots after receiving AstraZeneca shots.

The Johnson & Johnson COVID-19 vaccine has also been linked to a potential increased risk of Guillain-Barré syndrome (GBS) after reports emerged in July that around 100 people who received the single-dose vaccine developed the condition. GBS is an autoimmune disease that causes the immune system to target the nervous system. It can lead to muscle weakness or, in some cases, paralysis.

"Reports of adverse events following use of the Janssen COVID-19 Vaccine under emergency use authorization suggest an increased risk of Guillain-Barré syndrome during the 42 days following vaccination," the FDA said in a fact sheet on Emergency Use Authorization.