Reports of a rare type of blood clot following vaccination with both Johnson & Johnson and AstraZeneca's COVID-19 vaccines have emerged in recent weeks, and U.S. health regulators April 13 recommended that the use of the Johnson & Johnson vaccine be halted while six blood-clotting cases are investigated.
The AstraZeneca vaccine hasn't been authorized for use in the U.S., but several countries have restricted the use of that vaccine after reports of the unusual blood clots combined with low blood platelets. The European Medicines Agency has said the blood clots should be listed as a very rare side effect of the AstraZeneca vaccine.
Nine things to know about Johnson & Johnson and AstraZeneca's COVID-19 vaccines and blood clots:
- It's unclear who is most at risk for the blood clots. All six cases of blood clots after Johnson & Johnson's vaccine reported to the FDA have occured in women between the ages of 18 and 48, and there was a similar pattern seen in the blood clots afterAstraZeneca's vaccine, The Wall Street Journal reported. But there have been so few cases that experts haven't determined what the risk factors are.
- Both Johnson & Johnson and AstraZeneca's vaccines are viral vector vaccines, which use a different method to gain immunity than traditional vaccines. For the viral vector vaccines, scientists have isolated genes in the novel coronavirus that are responsible for making its spike proteins, according to the Journal. The genes are spliced into weakened, harmless versions of a virus, and when injected into a patient, the genetically engineered virus enters healthy cells where they produce the coronavirus spike proteins that then prompt the immune system to mount a defense against COVID-19. Both Pfizer and Moderna's vaccines use a different method, mRNA, to build immunity against the virus. Researchers are investigating whether the viral vector technology may play a role in the risk of blood clots, the Journal reported.
- The risk of getting a blood clot from COVID-19 is far higher than the risk of getting a blood clot from either Johnson & Johnson's or AstraZeneca's COVID-19 vaccine, CNBC reported. Purvi Parikh, MD, an infectious disease physician at NYU Langone Health in New York City, told CNBC April 13 that about 1 in 20 hospitalized COVID-19 patients develop a blood clot, as well as about 1 in 100 COVID-19 patients who aren't hospitalized.
- The FDA recommends that those who have received a Johnson & Johnson vaccine in the last three weeks look for symptoms such as severe headache, abdominal pain, leg pain or shortness of breath. If any of these symptoms are present, it's best to contact a healthcare provider, the Journal reported. Anne Schuchat, MD, principal deputy director at the CDC, told the Journal that the risk for blood clotting is very low for people who were vaccinated more than a month ago. People shouldn't be concerned about mild headaches and flu-like symptoms after the vaccine, which are common side effects, The New York Times reported.
- The clots appear to be caused by an intense immune system reaction to the vaccine that generates antibodies that activate blood platelets, researchers studying the blood-clotting reports after the AstraZeneca vaccine in Europe have said, according to The New York Times.
- Physicians in Germany and Norway have treated the blood-clotting after AstraZeneca's vaccine with blood-thinning drugs to stop the growth of the clots as well as with intravenous immune globulin, which can help eliminate the antibodies that may be causing the problem, according to the Times.
- U.S. federal health officials advised physicians against using heparin, a common blood thinner, to treat the blood clots, as the specific type of blood clots seen after the vaccinations closely resemble a rare syndrome caused by heparin, so the drug may make the condition worse, the Times reported.
- The blood-clotting events with Johnson & Johnson's and AstraZeneca's vaccines could be connected, Anthony Fauci, MD, director of the National Institute of Allergies and Infectious Disease, said April 14.
"There are some rather strong similarities about this with regard to the time frame following vaccination, particularly, importantly, the clinical syndrome of these clots together with low platelets, so there are a lot of similarities there that you just can't miss," he said, according to The Hill. - Roughly 1,000 to 2,000 blood clots occur daily in the U.S., and with several million people getting vaccinated per day, some of the blood clots may just be a coincidence and unrelated to the vaccines, the Times reported. However, the type of blood clot seen after the vaccinations are much rarer than typical blood clots.
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