THROMBOSIS WITH THROMBOCYTOPENIA SYNDROME (TTS)

Source: IndianExpress

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Context

• AstraZeneca, the producer of the AZD1222 vaccine, known as Covishield in India, has acknowledged a potential link between its vaccine and Thrombosis with Thrombocytopenia Syndrome (TTS), a rare condition characterized by low platelet counts and blood clot formation.

Details

• Covishield, manufactured by the Serum Institute of India (SII), has been widely used in India, with over 175 crore doses administered.
• The acknowledgment came in response to a lawsuit filed in the United Kingdom, where AstraZeneca is being sued over health claims related to its vaccine.
• While denying a generic link between the vaccine and TTS, AstraZeneca admitted the possibility of TTS occurring in "very rare cases."

Historical Context

• Concerns over blood clotting associated with AstraZeneca's vaccine have been reported since its rollout.
• In January 2021, the Indian government issued cautionary guidelines for Covishield administration to individuals with low platelet counts.
• Several European countries temporarily suspended the use of AstraZeneca's vaccine in March 2021 following reports of blood clotting incidents.
• The World Health Organization (WHO) noted cases of TTS post-vaccination with Covishield and Vaxzevria, albeit at very low rates.

Incidents in India

• In May 2021, the Indian government reported 26 potential thromboembolic events post-Covishield administration.
• The incidence rate of potential thromboembolic events was calculated at 0.61 cases per million doses administered.
• More recent data indicated at least 36 confirmed cases of TTS linked to Covishield, with 18 reported deaths.

Government Response

• The Union Health Ministry termed the risk of blood clotting post-Covishield vaccination as "minuscule" and highlighted the vaccine's positive benefit-risk profile.
• Covaxin, India's indigenous vaccine, did not report potential thromboembolic events.
• Scientific literature suggests a lower risk of blood clotting in individuals of South and Southeast Asian descent compared to those of European descent.

WHO Recognition

• In 2023, the WHO included Vaccine-induced Immune Thrombotic Thrombocytopenia (VITT) in its classification of TTS.

About TTS

• Thrombosis with thrombocytopenia syndrome (TTS) is a rare but serious condition characterized by abnormal blood clotting (thrombosis) and low platelet counts (thrombocytopenia).

Causes:

• Vaccine-Induced: TTS has been primarily associated with adenovirus vector-based COVID-19 vaccines, such as the AstraZeneca and Johnson & Johnson vaccines. It is believed to result from an immune response triggered by the vaccine that leads to platelet activation and clot formation.
• Other Triggers: TTS can also occur in response to other factors, such as certain medications, infections, or autoimmune conditions, although these cases are less common.

Symptoms:

• Blood Clots: Patients with TTS may develop blood clots in various parts of the body, including deep vein thrombosis (DVT), pulmonary embolism (PE), cerebral venous sinus thrombosis (CVST), and arterial thrombosis.
• Thrombocytopenia: Low platelet counts are a hallmark feature of TTS and may manifest as easy bruising, petechiae (small red or purple spots on the skin), or prolonged bleeding from minor injuries.
• Other Symptoms: Patients may experience nonspecific symptoms such as fatigue, weakness, shortness of breath, and abdominal pain.

Diagnosis:

• Physicians assess patients for signs and symptoms suggestive of TTS, including a history of recent vaccination or other potential triggers.
• Blood tests are conducted to measure platelet counts, assess coagulation parameters (such as D-dimer levels), and detect antibodies associated with TTS.
• Imaging modalities, such as ultrasound, CT scans, or MRI, may be used to visualize blood clots and assess their location and extent.

Treatment:

• Patients suspected of having TTS require prompt evaluation by healthcare professionals to confirm the diagnosis and initiate appropriate treatment.
• Anticoagulant medications, such as heparin or direct oral anticoagulants (DOACs), are commonly used to prevent the progression of blood clots and reduce the risk of complications.
• In severe cases of thrombocytopenia or active bleeding, platelet transfusions may be necessary to restore platelet counts and control hemorrhage.
• Some patients with vaccine-induced TTS may benefit from immunomodulatory treatments, such as intravenous immunoglobulin (IVIG) or corticosteroids, to suppress abnormal immune responses.

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Sources:

IndianExpress

PRACTICE QUESTION Q.  Examine the implications of AstraZeneca's acknowledgment of a potential link between the vaccine and TTS, considering both public health concerns and regulatory responses. How should governments balance the risks and benefits of COVID-19 vaccination amid emerging safety concerns like TTS? (250 words)