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Johnson and Johnson Vaccine Paused

 The Cause of the Pause: Johnson and Johnson Vaccine
    
    As of April 12, 2021, 6.85 million doses of the Johnson and Johnson vaccine have been administered in the United States. On April 13, the Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA) recommended a pause in the distribution of the Johnson and Johnson vaccine. This pause was due to a small number of reports of a rare type of blood clot in individuals after they received the Johnson and Johnson COVID-19 vaccine. Similar blood clotting events have also been reported in recipients of the AstraZeneca vaccine in European countries. Some may be wondering, what exactly are these rare blood clots and what effect does the Johnson and Johnson vaccine have on them? Do the Pfizer and Moderna vaccines have a similar effect? Should I be concerned if I received the Johnson and Johnson vaccine? Using reports and data from the CDC, FDA, and papers published in the New England Journal of Medicine, this post analyzes the reported adverse events and other details behind the pausing of the Johnson and Johnson vaccine.

Thrombotic Events and Thrombocytopenia in Patients

    As reported in the Vaccine Adverse Event Reporting System, 6 individuals in the U.S. suffered from a rare type of blood clot called cerebral venous sinus thrombosis which was seen with thrombocytopenia, or low levels of blood platelets, after receiving the Johnson and Johnson vaccine. According to the reports, all six cases occurred in women who were aged between 18 and 48 years. Initial symptom onset ranged from 6-13 days after vaccination. All patients reported symptoms of headache while one patient also experienced abdominal pain, nausea, and vomiting. Four patients developed a brain hemorrhage, or bleeding in the brain, and neurological symptoms including focal weakness, inability to understand or express speech, and visual disturbance. One woman died. Because these specific blood clots and adverse events developed after the Johnson and Johnson COVID-19 vaccination, the CDC and FDA have paused the distribution of the Johnson and Johnson vaccine to ensure that it is safe. In the direct words of the CDC, "We do not know enough yet to say if the vaccine is related to or caused this health issue. To be extra careful, CDC and FDA recommend that the vaccine not be given until we learn more."

Why Johnson and Johnson?

    As of April 13, 2021, over 180 million people have received the Pfizer and Moderna COVID-19 vaccines but there have been no reported cases of the blood clot issue in as seen with the Johnson and Johnson vaccine. However, similar reports of thrombotic events and thrombocytopenia have been seen with recipients of the AstraZeneca vaccine. Why is that?

    Unlike the mRNA based Pfizer and Moderna vaccines, the Johnson and Johnson and AstraZeneca vaccines are adenovirus based. These vaccines use a weakened form of an adenovirus that encodes a SARS-CoV-2 spike protein which then generates an immune response. Although the AstraZeneca vaccine uses a chimpanzee adenoviral vector and the Johnson and Johnson vaccine uses a human adenoviral vector, both have been linked with rare blood clotting events. A study published in the New England Journal of Medicine examined the 11 patients in Germany and Austria who developed thrombotic events or thrombocytopenia after receiving the AstraZeneca vaccine. Similar to the 6 reported Johnson and Johnson cases, all patients in the AstraZeneca-related study were women aged 22-49 years with a symptom onset beginning 5-16 days after vaccination. The study found that all patients tested positive for the heparin-PF4 antibody, a platelet-activating antibody that can induce thrombotic events and thrombocytopenia. Another study conducted in Oslo also reached similar findings regarding PF4-antibodies with 5 health care workers who experienced rare blood clotting events within 10 days of AstraZeneca vaccination; this further highlights the conclusions of the aforementioned study. Because the AstraZeneca and Johnson and Johnson vaccines are both adenovirus-based and have resulted in rare cases of blood clotting, it can be inferred that the Johnson and Johnson vaccine also relates to the heparin-PF4 antibody which can lead to rare thrombotic events. 

What now?

   If you received the Johnson and Johnson COVID-19 vaccine, the CDC says "your risk of developing a blood clot is very low." However, if symptoms such as severe headache, backache, new neurologic symptoms, pain in the abdomen, shortness of breath, leg pain or swelling, or easy bruising develop 1-2 weeks after vaccination, medical care should be sought right away. 

    It is important to remember that these blood clotting cases after vaccination are extremely rare. Overall, the prevalence of vaccination complications are very low relative to the benefits of preventing the spread of the coronavirus. While the Johnson and Johnson vaccine is paused in the U.S. for extra precautions until more is learned (AstraZeneca is not administered in the U.S.), the Pfizer and Moderna vaccines are still in distribution and have a good safety record. For more information about the COVID-19 vaccines check out the CDC or read the other vaccine-related posts on this blog.

Sources

1. Greinacher, Andreas, et al. “Thrombotic Thrombocytopenia after ChAdOx1 NCov-19 Vaccination.” New England Journal of Medicine, 9 Apr. 2021, doi:10.1056/NEJMoa2104840.

2. Marks, Peter. “Joint CDC and FDA Statement on Johnson & Johnson COVID-19 Vaccine.” U.S. Food and Drug Administration, 13 Apr. 2021, www.fda.gov/news-events/press-announcements/joint-cdc-and-fda-statement-johnson-johnson-covid-19-vaccine.

3. “Recommendation to Pause Use of Johnson & Johnson's Janssen COVID-19 Vaccine.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 13 Apr. 2021, www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/JJUpdate.html.

4. Schultz, Nina, et al. “Thrombotic Thrombocytopenia after ChAdOx1 NCov-19 Vaccination.” New England Journal of Medicine, 9 Apr. 2021, doi:10.1056/NEJMoa2104882.

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