How Concerned Should You Be About Getting Thrombocytopenia After a COVID-19 Vaccine?

Experts looked into possible links between the rare blood disorder and COVID-19 vaccinations.

Millions of Americans have been getting their COVID-19 shots, and while some people have pain, fatigue, or fever afterward, most side effects are mild. However, there were reports of an expected side effect: a rare blood disorder—a condition called immune thrombocytopenia (ITP)—which occurred in a small number of people after getting their COVID-19 vaccine in February 2021.

The New York Times broke news about problems a few patients experienced after vaccination, with ITP being one of them. This prompted commentary, published in a February 2021 issue of the American Journal of Hematology, about the potential relationship between ITP and the Pfizer and Moderna COVID-19 vaccines. The researchers said that it was possible for ITP to be due to the vaccine, but more data would be necessary to determine any concrete connections.

Thus, with the push for COVID-19 vaccines and ITP being a serious condition, how worried should you be about having ITP as a side effect of COVID-19 vaccination? Here's what you need to know.

What Is Immune Thrombocytopenia?

Thrombocytopenia is a medical term meaning low platelet count. Thrombocytes, or platelets, are a type of blood cell that helps blood to clot, the National Heart, Lung, and Blood Institute (NHLBI) says. There are different types of thrombocytopenia with different causes.

With immune thrombocytopenia (ITP) in particular, the body's immune system attacks and destroys its own platelets, per the NHLBI, and produces fewer platelets than normal. "What happens is that, for an unknown reason, your immune system makes antibodies to platelets," explained James Bussel, MD, professor emeritus of pediatrics at Weill Cornell Medicine in New York City and a leading researcher in the field, adding that there are several different theories about why that may happen. It's been known to occur with other vaccines too, Dr. Bussel added.

Normally, platelet counts range between 150,000 and 450,000 per microliter of blood, Dr. Bussel said. It's possible to have a lower-than-normal platelet count and not have symptoms. However, when the platelet count is low enough and symptoms do occur, bruising and bleeding are common, Dr. Bussel added. Pin-sized reddish-purplish spots called petechiae can appear on the skin. Nosebleeds, bleeding from the mouth, and heavy periods can also occur. Most people respond to treatment with intravenous immunoglobulin and/or steroids, Dr. Bussel added.

How Did Immune Thrombocytopenia Become Connected With COVID-19 Vaccines?

The US Food and Drug Administration (FDA) says anyone, including health care providers, patients, their family members, and state immunization programs, can report adverse events that occur after someone is vaccinated using the federal government's Vaccine Adverse Event Reporting System (VAERS.)

Both FDA and the Centers for Disease Control and Prevention (CDC) review data reported to the VAERS. FDA characterizes the reporting system as "a valuable tool" for keeping tabs on patient safety after vaccines go to market. In relation to the Times report, 36 reports of ITP had been submitted to the VAERS.

As Dr. Bussel told Health in February 2021, only 19 of the reports to VAERS represented "clear cases" of ITP. The cases were equally divided between the two COVID-19 manufacturers, and they didn't seem to be age- or gender-specific. In the American Journal of Hematology commentary, Dr. Bussel and his colleagues noted that the incidence of ITP after COVID-19 vaccination "appears either less than or roughly comparable to what would be seen if cases were coincidental following vaccination."

Why You Shouldn't Be Worried About Getting the COVID-19 Vaccine

In clinical trials of the Moderna and Pfizer vaccines, which involved roughly 30,000 and 44,000 people, respectively, serious adverse events were rare and occurred at similar rates among trial participants whether they received the vaccine or a placebo. Trial data from the two pharmaceutical companies, published in separate reports in the New England Journal of Medicine, did not mention thrombocytopenia among adverse events recorded during clinical trials.

While it may not have surfaced among the 74,000 trial participants, as more people get vaccinated, a case of ITP may pop up here and there. "When millions are vaccinated, there inevitably will be some people who develop ITP," Dr. Bussel said.

Additionally, the Platelet Disorder Support Association (PDSA), a nonprofit patient support group, noted that the risk of getting ITP or vaccine-induced thrombocytopenia "is less than 1 in 100,000." The PDSA also said that there was a lower risk of developing ITP with Pfizer and Moderna vaccines.

Research is still ongoing to learn more about cases of ITP in patients receiving the COVID-19 vaccines. For example, a Blood Advances review published in March 2022 found that risk factors for developing ITP after getting a COVID-19 vaccination was associated with lower platelet counts, being of a younger age, and the current ITP treatment.

Still, the risk of ITP appears to be much lower than the risk of developing COVID-19. "This should not provide a reason for people not to be vaccinated," Dr. Bussel said. "And if they have any uncertainties, they should consult with their physician."

For those who already have ITP, the PDSA also recommended that individuals may choose to consult their hematologist or another physician before proceeding with getting vaccinated.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.

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