Over two dozen cases of the rare blood disorder thrombocytopenia have been reported in people who have received COVID vaccines in the U.S. However, a link between COVID vaccines and the disease that affects platelets has not been proven.

The Vaccine Adverse Event Reporting System (VAERS), which is jointly run by the U.S. Centers for Disease Control and Prevention and the U.S. Food and Drug Administration, is recording any potential side-effects experienced by people after they receive a vaccine.

By the end of January, 32 cases of a decreased platelet count, 14 cases of thrombocytopenia, and 11 cases of immune thrombocytopenia were recorded in people who had received either Pfizer or Moderna COVID vaccines in the U.S.

More than 43 million vaccine doses have been administered in the U.S.

Last month, a man in Florida died after developing thrombocytopenia days after getting vaccinated against COVID. 56-year-old Miami-based doctor Gregory Michael started displaying the symptoms of a form of the disorder called idiopathic thrombocytopenic purpura (ITP) days after receiving the Pfizer-BioNTech vaccine. He died two weeks later from a brain hemorrhage.

Newsweek has contacted Pfizer and Moderna for comment about the cases. Pfizer told The New York Times "at this time, we have not been able to establish a causal association with our vaccine" and that it was collecting relevant information to share with the FDA.

Moderna told the newspaper it "continuously monitors the safety of the Moderna Covid-19 vaccine using all sources of data."

Experts have previously told Newsweek that rare side-effects may emerge as the vaccines are rolled out across large populations, but the benefits far outweigh the risks.

What is thrombocytopenia?

Thrombocytopenia is a rare disorder that lowers the number of platelets in your blood.

Platelets, which are also known as thrombocytes, are cells that are essential for making blood clot, a process that stops you from continually bleeding from the site of an injury.

According to the Platelet Disorder Support Association (PDSA), around 100,000 people in the U.S. have the condition.

What causes thrombocytopenia?

Thrombocytopenia can run in families. However, it can also be triggered as an immune response to infection, disease or medication. In this instance the condition is known as immune thrombocytopenia, or idiopathic thrombocytopenic purpura (ITP).

ITP causes white blood cells, which create antibodies that fight infection, to instead attack your body's own platelets.

What are the symptoms of thrombocytopenia?

Symptoms of thrombocytopenia include bruising above areas of bleeding under the skin, flat red spots, and the presence of blood in your stool or urine.

However, these symptoms may only appear when your platelet count has fallen to dangerously low levels.

A normal platelet count ranges from 150,000 to 450,000 platelets per microliter of blood, but symptoms may only appear when the platelet count falls below 10,000 per microliter.

In this instance, bleeding or bruising may occur with no obvious cause.

A dose of the Pfizer Covid-19 vaccine is administered at Cal Poly Pomona University in Pomona, California on February 5, 2021. A Florida man died from ITP in January days after receiving the shot. Frederic J. Brown/AFP via Getty Images