Immune Thrombocytopenia Purpura (ITP, previously known as Idiopathic Thrombocytopenia Purpura) risk post vaccination

Immune Thrombocytopenia Purpura (ITP, previously known as Idiopathic Thrombocytopenia Purpura) risk post vaccination

Recently, a post was shared with me where a wife was sharing concerns about the novel COVID-19 vaccines and her husband’s death from Immune Thrombocytopenia (ITP), shortly after his immunization. You could feel the pain the wife was feeling and the anguish over the loss of her husband, and her heartfelt concerns about the relationship between his recent COVID-19 vaccination and the subsequent onset of ITP.

Even though her post is public, we will refrain from linking her post here, as she needs her personal privacy and there is no need to give a direct link which could be used to mob her by individuals who are anti-vaccine. If we see links to the post or names in the comments below, they will be removed to protect her privacy.

So let’s talk about ITP, the risk of ITP, the relationship between vaccines and ITP, and how the occurrence of ITP post-COVID vaccination is unlikely to be related to the vaccine itself, and why.

What is Idiopathic (Immune) Thrombocytopenia Purpura

As with any topic in medicine, as our understanding of a topic increases, we often will see changes in terminology, definitions, and diagnoses.

ITP is no different than any other topic within medicine. For those of us who have been in the medical field for decades, we recognize ITP as the acrostic for Idiopathic Thrombocytopenia Purpura.

1. Idiopathic is the medical term meaning “unknown cause,” and is describing how we aren’t exactly sure what causes the disease.

3. Thrombocytopenia is low platelet counts (platelets are an essential component of the bodies ability to both initiate and form clots), and can be caused by countless factors including cancer, certain medications, genetic diseases, certain plants/herbs, etc.

5. Purpura is describing the scattered superficial bruising (often without a known cause) often worse in the arms/legs and often has irregular borders which is seen with low platelet counts.

So the old definition of ITP described a specific bruising pattern, caused by low platelet counts, which exists without a known cause.

The more modern definition of ITP is Immune Thrombocytopenia Purpura, which shows our increased knowledge of the topic, and how that our understanding has grown to understand that this disease is often caused by an autoimmune disorder which attacks platelets. The rash and low platelet counts remain the same, it is our understanding of the mechanisms which cause ITP has changed.

The risk for ITP:

ITP is seen very rarely in the general population. In children, ITP presents very acutely, where in contrast, it’s almost always chronic in adults. The usual cause for ITP in children is certain bacterial and viral infections (HIV, HepA, HepB, Mumps, Influenza, etcetera) and is often self limiting, recovering without treatment. In adults, the disease shares similar causes as children, and also includes recent pregnancy, certain drugs, and immune disorders like Systemic Lupis (SLE). Even in chronic instances, ITP is rarely fatal and often is treatable with steroids, and less frequently with immune globulin therapy.

In children (ages 1-18), ITP is seen an average of 4.2 per 100,000 children per year. These numbers peak between the ages of 2-5 and the lowest is between the ages of 13-17 (2.4 per 100,000). This would correlate with the cessation of breastfeeding (and maternal protective antibodies) and the introduction of many viral infections. The vast majority of vaccinations occur prior to age 2, so it would be a false assumption that vaccines are the cause for the majority of ITP cases in children.

In adults, ITP occurs at a significantly lower rate (about 1.2 per 100,000) with the majority of these cases occurring when an individual is over 55 years of age (rate almost double or about 2.4 per 100,000). ITP in adults is almost exclusively chronic, and the risk of bleeding and mortality is higher since the duration of low platelet counts are longer.

In children, the mortality rate for ITP is very low, as the onset and duration of the thrombocytopenia is sudden and short lived for the vast majority of children (between 80-90% resolve within 2 months of onset). The data I have seen approximates that about 2 children die per year of ITP (about 800 children die of drowning each year to put it into perspective).

With adults, the mortality rate is significantly higher, as the duration is chronic for the vast majority of cases. With any chronic disease process, it’s difficult to take a snapshot measurement of death rates, so we measure the mortality risk against similar populations and measure this as a hazard ratio. This allows us to see if the chronic disease is associated with an increase in risk, decrease in risk (almost never), or no change in mortality risk. With ITP, the adjusted hazard ratio is 1.5 (CI 95%, 1.2 – 1.82) for all ages, or a 50% increase in comparison to non-ITP patients.

Vaccines and ITP:

To be able to understand ITP and vaccines, we need to be able two different questions:

1. What is the rate of ITP in the disease being prevented vs the rate of ITP post vaccination?

2. Does the rate of ITP differ significantly from normally occurring rates?

These two questions allow us to estimate whether the vaccine has an avoidance capacity for ITP or whether ITP occurs at a consistent rate with those who aren’t vaccinated. It also allows us to look at whether ITP occurs more frequently with vaccines. This is a standard way of comparing the risk for something after an intervention by comparing the risks/benefits to determine a hazard ratio.

ITP and Influenza/Coronavirus Infections and post Influenza/COVID vaccination.

So let’s talk about ITP in Influenza and ITP in Coronaviruses, as this is both one of the common causes of ITP and the inferred cause by the original poster.

Influenza infection commonly causes ITP (some research believes that up to 25% of influenza B infections have decreased platelet counts) and is one of the most common causes of ITP in children. Coronaviruses, on the other had, do not typically cause thrombocytopenia, they cause thrombocytosis (higher platelet counts). Since SARS-CoV-2 (and other coronaviruses) do not show a tendency towards thrombocytopenia, and in fact tend to cause the opposite effect, there isn’t a direct relationship with the infection and ITP risk.

Since as much as 25% of Influenza infections cause ITP, it’s unsurprising that influenza vaccinations have also been linked to ITP. (Influenza induced ITP is believed to be caused by the similarities between certain proteins on the influenza Hemaglutanin (HA) protein being similar to proteins on the platelet surfaces.)

When we compare the incidence of ITP post-vaccination compared to the actual disease, ITP occurs infrequently with influenza vaccinations (There are only a handful of case reports which identify an influenza vaccine as potentially linked to childhood influenza immunization vs. high percentages of hospitalized influenza infections having thrombocytopenia). When they did a case cohort study of ITP post vaccinations, the adjusted Odds Ratio was 0.99 (a 1 is no difference in occurrence rate for ITP).

Since there isn’t a potential link between coronavirus infections and ITP, we don’t have a direct link between the vaccine and ITP. Without this link, it’s highly unlikely that the vaccine is responsible for the ITP. Since the vast majority of adult ITP is chronic, not acute. This, along with the lack of a direct link between the disease and ITP, makes it highly likely that the ITP was chronic and the occurrence of ITP exacerbation was unrelated to the vaccine.

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