One Clot Is All It Takes

The U.S. Centers for Disease Control and Prevention paused the use of the Johnson & Johnson COVID-19 vaccine after reports of a rare blood clot but has since lifted the pause, insisting that the benefits of the vaccine outweigh the risks.

Reading Time: 4 minutes

Cover Image
By Joanna Meng

As millions of joyous vaccine recipients flooded social media with their “I got vaccinated” stickers, relieved that their battle with COVID-19 was finally over, their celebration quickly turned to panic when scientists reported six cases of cerebral venous sinus thrombosis (CVST), an extremely rare but harmful type of blood clot, in those who received the Johnson & Johnson (J&J) vaccine. It was news no one wanted to hear—especially for those who had already received that vaccine. Once again, ongoing vaccine distrust heightened, obstructing the enduring battle to return to normalcy.

Despite the recent rise of concerns regarding vaccine safety and efficacy in the U.S., these doubts had already begun circulating in European nations, where the AstraZeneca vaccine, which shares the same technology as the J&J vaccine, was reported to have caused clotting disorders in over 30 recipients, 15 of whom died. While the U.S. boasted the vaccine’s success, European nations suspended its administration. Several scientists, including German clotting specialist Andreas Greinacher, pointed fingers at the vaccine, jeopardizing the keystone in the push to immunize the world. Greincacher named the condition vaccine-induced prothrombotic immune thrombocytopenia (VIPIT). It had a striking resemblance to an existing blood clotting syndrome called heparin-induced thrombocytopenia (HIT), which leads to low platelet counts as an immune response to heparin, an anticoagulant or blood thinner. While low platelet counts normally cause bleeding since the body cannot form clots without platelets, HIT causes unstoppable clotting instead. In the case of CVST, the clotting prevents blood from draining out of the brain and leads to hemorrhage, a type of stroke. As the news disseminated, confidence in the vaccine decreased, and concern that the vaccine could be potentially life-threatening was revived.

Nearly a month later in the U.S., similar cases of the disorder were reported in six women who received the J&J shot, leaving one in critical condition and another dead. The cases were all reported among women under the age of 50, within two weeks of receiving the vaccine. Since the condition occurs in response to heparin, the main treatment of blood clots, the Centers for Disease Control strongly discouraged its usage. Instead, intravenous immunoglobulin, an anticoagulation medication, was recommended to treat the disorder. Health officials also insisted there was no need to worry as the cases were extremely rare with less than a one out of one million chance, and there was no clear correlation between the blood clots and the vaccine. Despite this, the Food and Drug Administration (FDA) placed a temporary pause on the J&J vaccine administration to conduct an investigation.

The pause spread worldwide, from Australia to South Africa, where a new deadly variant was ravaging the population. It also sparked debate among health officials on potential risks introduced by the pause, including greater vaccine hesitancy, and whether the pause was necessary.

As more cases emerged, with over 300 among the 33.6 million recipients of the AstraZeneca vaccine and 15 out of the eight million J&J shot recipients, scientists faced pressure to find the cause. Building off of Greinacher’s research, studies suggested that the adenovirus, a key ingredient in the J&J and AstraZeneca vaccines used to deliver genetic material to the cells, led to the development of antibodies targeting platelet factor 4, a protein responsible for coordinating blood clotting. By contrast, the Moderna and Pfizer vaccines use mRNA technology to deliver instructions to the cells. Though, in rare instances, the adenovirus triggers a harmful immune response that develops into a HIT-like disorder with low platelet counts and large blood clots, only a microscopic percentage of inoculated people develop this immune response. Scientists have also speculated that some vaccinated people who developed the clots would have developed them regardless of whether or not they were vaccinated.

Most importantly, a major finding of the studies concluded that the benefits of the vaccine continue to outweigh the risks, as it provides protection against getting sick or dying from COVID-19 and reduces the risk of hospitalizations. The risk of thrombocytopenia from vaccination is lower than the risk of developing thrombocytopenia in the general population. Moreover, the risk of VIPIT, one in a million, is diminutive compared to the chances of being hospitalized with COVID-19, which is one in 100. This reveals the issue of vaccine hesitancy, which leaves millions exposed to the risks while thousands of doses go to waste due to the vaccine’s short shelf-life after thawing. While the cases appear to be more common in women, data suggests that this may be a mere coincidence.

After a brief but thorough safety review, the FDA and Centers for Disease Control lifted the pause on the J&J vaccine administration, reinforcing confidence in the vaccine’s safety. Since then, the vaccine has returned to vaccination sites, now with an added label for the potential risk of the blood-clotting disorder. Though overall vaccination has slowed down, over 50 percent of American adults have received at least one shot of the COVID-19 vaccine, shy of the 70 to 85 percent needed for herd immunity. Many European countries have also lifted the suspension of the AstraZeneca vaccine, emphasizing that the benefits outweigh the risks.

Though there is no need to be concerned, it is important to know about the blood clot disorder. Learning the risk factors is the best way to decrease the risk of becoming susceptible to it. Such risk factors include contraceptives, anti-inflammatory drugs, hormone replacement therapy, pregnancy, COVID-19, smoking, dehydration, and air travel. It is also important to look out for symptoms such as persistent headaches, a full-body rash, shortness of breath, pain in the leg or abdominal region, and swelling, and if any are present, one should immediately contact a doctor.

The world needs the vaccine. As necessary as it was to pause its rollout and study the illness, it was far more essential to lift the pause and resume the vaccine’s rollout. Studies have reinforced that the risks are vanishingly tiny and are not worth refusing the vaccine nor losing sleep over. Rather, a loss of sleep may increase your risks more than the vaccine. While this moment is precarious in a seemingly endless pandemic, it has once again been proven that the public should trust the vaccine, our only weapon to end the pandemic.