As of the end of January 2021, 36 cases of the blood disorder Immune thrombocytopenic purpura (ITP) have been reported to the U.S. government’s Vaccine Adverse Event Reporting System (VAERS). The cases have involved both the Pfizer-BioNTech and the Moderna vaccine, which are the two vaccines currently approved for emergency use in the U.S. 

It is too soon to know whether or not the timing of ITP and COVID-19 vaccination were coincidental in these cases. It's also not clear if vaccination led to an exacerbation of pre-existing unrecognized ITP, or if the vaccination caused ITP.

Some hematologist experts in ITP have noted that they suspect the vaccine played a role in the onset of ITP, particularly given that viral infections can cause ITP, and given that similar reactions have occurred after pneumococcal, MMR, and other vaccinations. However, if there is an association, these cases are likely to be extremely rare. They may also be the result of a predisposition to ITP that is unknown before the onset of the condition, especially as it’s possible to have low platelet count without symptoms. 

Given the low number of cases, it is likely more cases would be needed to better understand any association between the vaccines and ITP and to establish a causal link, if there is one. Pfizer and Moderna have both put out statements that they are continuing to collect and monitor safety data from the public, and Pfizer has specifically stated “we have not been able to establish a causal association with our vaccine.

Immune thrombocytopenic purpura (ITP), is a disorder of the blood that is characterized by a decrease in platelets (cells that help to stop bleeding) within the blood. A decrease in platelet count can result in easy or excessive bruising, bleeding from the gums or nose, and internal bleeding. A rare complication of ITP is bleeding into the brain, which can be deadly.

ITP typically affects approximately 0.01% of the adult population. The condition, which is generally treatable, emerges when one’s immune system attacks platelets or the cells that create platelets. The reasons for why the immune system begins attacking platelets or the cells that create them is not well known; sometimes it follows a viral illness, for instance, and can last for months or become chronic and persist for years. 

In early January of 2021, a Florida physician died from complications of immune thrombocytopenia (ITP) two weeks after receiving the COVID-19 vaccine. He went to the hospital three days after receiving the first dose of the Pfizer-BioNTech vaccine and later passed away of a brain hemorrhage, after doctors were unable to get his platelet count up. ITP is rare, and internal bleeding of the brain leading to fatality is even more rare, but the story has stoked fear and uncertainty in the public regarding the Pfizer-BioNTech and Moderna vaccines, particularly as more cases surrounding COVID-19 vaccinations continue to emerge. 

The benefits of the COVID-19 vaccine for people without preexisting ITP strongly outweighs the risks of avoiding vaccination out of fear of ITP. ITP has also been observed as a possible reaction to COVID-19 among those without the vaccine at much higher rates than following the vaccine. Up to 10% of patients with mild disease and 20% in those who are severely affected. For those with preexisting ITP, while the risk is a bit greater, the benefits of receiving the vaccine still outweigh the risks; however, it is best to consult with your hematologist and obtain a platelet count before doing so.