Immune thrombocytopenia (ITP)

Background

Immune thrombocytopenia, previously known as idiopathic thrombocytopenia purpura (ITP) and still commonly referred to as ITP, is an uncommon autoimmune condition in which the body’s own immune system attacks platelets (the cells found in the blood which help it clot). The body produces antibodies that attack and destroy platelets; this results in decreased platelet numbers and can cause symptoms such as bruising, petechiae (pin-point red spots on the skin) or bleeding (e.g. nose bleeds or bleeding from the gums). Some people have no symptoms at all.

ITP is most often triggered by a viral illness occurring in the weeks prior to ITP symptoms developing. ITP can be acute (lasting less than 12 months) or chronic (lasting longer than 12 months), with acute ITP far more common in children and chronic ITP far more common in adults. The symptoms of acute and chronic ITP are the same. Approximately one in every 10,000 children will be affected by ITP.

It is not uncommon for cases of ITP to be discovered by chance. In some instances, ITP may go away without any treatment. However, when platelets are very low or there are symptoms of bleeding, treatment may be needed. Corticosteroids and intravenous immunoglobulin are the most common forms of initial treatment.

ITP and vaccines

As ITP is an immune-mediated condition (a disease thought to result from an abnormal immune system response), it can be triggered by the body’s immune response to vaccination. While there are some small studies that suggest a possible increased risk of ITP with certain vaccines (such as influenza, HPV, polio and pneumococcal vaccines), ITP has only been found to be associated with measles, mumps and rubella (MMR)-containing vaccines (including MMRV), and COVID-19 vaccines. It is important to note that there is a much higher risk of ITP associated with infection compared to the risk associated with vaccination. 

ITP and measles-mumps-rubella (MMR) vaccines

MMR vaccines have been associated with ITP, with the risk estimated at approximately 1 in 25,000 vaccinations.  The risk following vaccination is much lower than the risk associated with natural measles or rubella infections. Therefore, patients with a history of ITP are still recommended to receive the MMR vaccine in line with the National Immunisation Program (NIP), despite the small risk of relapse, to protect against disease.

In children with a history of either non-vaccine or vaccine-associated ITP who have already received their first dose of MMR vaccine, vaccine titres can be checked to determine the need for dose 2. If the child displays full immunity, then no further MMR-containing vaccines should be given (e.g. administer varicella alone at 18 months); if the child does not have adequate immunity, then the child should receive dose 2 as scheduled.

ITP and COVID-19 vaccines

New onset or exacerbation of existing ITP has been reported following COVID-19 vaccination, with mRNA vaccines (Comirnaty (Pfizer) and Spikevax(Moderna)) and with Vaxzevria (the AstraZeneca vaccine which is no longer in use). This link continues to be investigated; however, the risk is low. Vaccination is important to reduce the risk of severe COVID-19 disease. It is important to note that ITP can also be triggered by COVID-19 infection itself. 

Recommendations

Individuals who have previously been diagnosed with non-vaccine or vaccine-associated ITP (acute or chronic) are recommended to proceed with vaccination as per the NIP.

There is limited data suggesting that chronic ITP may worsen following vaccination in those with existing chronic ITP (whether non-vaccine or vaccine-associated). Note that the risk of ITP worsening is likely higher if an individual with chronic ITP is infected with a virus than it is following vaccination. If clinical symptoms worsen post-vaccination (days to weeks), then monitoring of platelets and escalation of therapy may be required. Signs and symptoms of worsening ITP include:

• easy bruising

• nose bleeds or bleeding gums

• very heavy periods

• petechiae (pin-point red spots on the skin).

Where a diagnosis of ITP is made with a temporal association to vaccination, a report should be made to SAEFVIC for investigation and management of future vaccines.

Precautions

Vaccination following the receipt of immunoglobulin (IVIg)

Administration of live-attenuated vaccines such as measles-mumps-rubella-varicella and measles-mumps-rubella must be delayed following the administration of intravenous immunoglobulin (IVIg) as the transfusion of IVIg can affect the immune response to the vaccine. For more information, refer to MVEC: Live-attenuated vaccines and immunoglobulins or blood products.

Resources

• American Society of Hematology: 2019 guidelines for immune thrombocytopenia 
• RCH Clinical practice guidelines: Immune thrombocytopenic pupura
• Better Health: Immune thrombocytopenia purpura (ITP) 
• Gordon SF, Clothier HJ, Morgan H, et al. Immune thrombocytopenia following immunisation with Vaxzevria ChadOx1-S (AstraZeneca) vaccine, Victoria, Australia. Vaccine. 2021;39(48):7052-7057. doi:10.1016/j.vaccine.2021.10.030 
• Miller E, Waight P, Farrington CP, Andrews N, Stowe J, Taylor B. Idiopathic thrombocytopenic purpura and MMR vaccine. Arch Dis Child. 2001;84(3):227-229. doi:10.1136/adc.84.3.227 
• Black C, Kaye JA, Jick H. MMR vaccine and idiopathic thrombocytopaenic purpura. Br J Clin Pharmacol. 2003;55(1):107-111. doi:10.1046/j.1365-2125.2003.01790.x 
• Rinaldi M, Perricone C, Ortega-Hernandez OD, Perricone R, Shoenfeld Y. Immune thrombocytopaenic purpura: an autoimmune cross-link between infections and vaccines. Lupus. 2014;23(6):554-567. doi:10.1177/0961203313499959 
• O’Leary ST, Glanz JM, McClure DL, et al. The risk of immune thrombocytopenic purpura after vaccination in children and adolescents. Pediatrics. 2012;129(2):248-255. doi:10.1542/peds.2011-1111