Oxford-AstraZeneca Covid-19 vaccine: Side-effects from mild to Blood Clot and Low Platelets Count

Vaxzevria is a vaccine, jointly developed by Oxford–AstraZeneca. Despite side-effects, many medical authorities like WHO, has been listed it for emergency use and is found to be safe and effective based on data from large-scale clinical trials.

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Many Covid-19 vaccine have been developed till date, showing many effects and side-effects on people. The Oxford–AstraZeneca COVID-19 vaccine are sold under the brand names Covishield and Vaxzevria. Vaxzevria is a two dose vaccine, given by intramuscular injection, which causes side-effects ranging from mild-to-moderate severity that people often experience after any vaccination, which generally resolve within 2 days. However, a type of side-effect i.e. rare blood clotting with decreased platelets counts, linked to this Covid vaccine has been surrounded by many controversies. It is given to individual of age 60 and above.

As per the data published in February, 2021, the vaccine has a 76% efficacy rate after first dose and increased to 81.3 after second dose.

On January 29, 2021, after a recommendation from the European Medicines Agency (EMA), the European Commission granted the vaccine “conditional marketing authorization” in the European Union for adults aged 18 years and older. The World Health Organization (WHO) issued the vaccine “emergency use listing” on February 15.

How does Vaxzevria works?

Vaxzevria is a viral vector vaccine, made up of another virus i.e. Adenovirus, that contains the modified gene, for making the spike protein present on the surface of Covid virus, which is required to enter the body’s cell. 

Since the adenovirus cannot reproduce in the vaccine, so does not cause disease. This vaccine does not contain the SARS-CoV-2 virus itself and so does not cause COVID-19 disease. 

Once it has been given, the vaccine delivers the modified gene into cells in the body. The cells will use up the gene to produce the spike protein. The person’s immune system will then recognize this protein as foreign substance and produce antibodies against it and activate T cells (white blood cells) to attack it. If a person again comes in contact with SARS-CoV-2 virus, their immune system will recognize it and defend the body against it.

Common side effects

According to the vaccine’s safety profile within the product information, the most common side effects include mild-to-moderate symptoms of one or more of the following:

  • fatigue (53.1%)
  • headache (52.6%)
  • muscle or joint pain (44% or 26.4%)
  • fever (33.6%)
  • chills (31.9%)
  • nausea (21.9%)

The percentages are based on reports from four clinical trials with a total of 23,745 participants.

  • In very rare case, blood clot along with decreased platelet counts have also been reported.
  • Pain and Irritation at injection site has also been reported in some people. 
  • Allergies like rash, hives, swelling, respiratory symptoms to some vaccine ingredients have also been seen. 
  • Anaphylaxis is also been observed but very rare. As per the reports from the Medicines & Healthcare products Regulatory Agency (MHRA), 455 (0.002%) out of 19.5 million were observed with an anaphylaxis-related adverse reaction, when administered the doses of Vaxzevria vaccine and people are advised to check the ingredients mentioned before vaccination.

As per Centers for Disease Control and Prevention (CDC), all the side-effects mentioned are similar to the side-effects of vaccines from the Pfizer-BioNTech and Moderna vaccines. 

The vaccine was first approved for use on 30 December 2020, in the UK vaccination program, and the first vaccination outside of a trial was administered on 4 January 2021. Since then the vaccine has been approved by several medicine agencies worldwide such as the European Medicines Agency (EMA), the Australian Therapeutic Goods Administration, and was approved in the list of an Emergency use by the World Health Organization (WHO). However, some countries have limited its use to elderly people at higher risk for severe COVID-19 illness due to the very rare risk of clotting problems in younger individuals

Controversy regarding blood clots

Later, in early March, several European countries temporarily put on hold the use of the AstraZeneca vaccine as in some cases, blood clots and decreased platelet counts have been found. In early March 2021, the Danish Health Authority put Vaxzevria use on hold, following reports of severe cases of blood clots.

The EMA noted that 30 cases of blood clots, or thrombosis, had occurred with Vaxzevria administration to around 5 million people in the European Economic Area, including one fatal case in Denmark. EMA also observed multiple types of thrombosis, including unusual cases of cerebral venous sinus thrombosis, which is a rare occurrence of blood clots in the brain.

However, on March 18, the EMA states that the vaccines are safe and effective over 60 years, the benefits continue to outweigh the risks by preventing SARS-CoV-2 infection.

According to the MHRA, in the United Kingdom, as of March 31, there had been 79 reports of blood clot with low platelets counts and all of which occurred after first dose administration, and 19 were fatal.

Although the regulatory agencies have not listed specific risk factors for blood clotting, the EMA suggests that the combined incidents of blood clots and low blood platelet counts may be a type of immune response. On 7 April 2021, the EMA concluded that unusual blood clots with low blood platelets should be listed as very rare side effects of Vaxzevria, suggesting as a potential event.

On 30 January 2021, the Health Minister in Vietnam, approved the AstraZeneca vaccine for use, becoming the first vaccine to be approved in Vietnam.

Symptoms related to Blood Clots

There are some symptoms observed which are related to blood clot, which includes:

  • Abdominal pain
  • Chest pain
  • Leg swelling
  • Shortness of breath
  • Neurological symptoms, including headaches and blurred vision

Currently, 83 countries have authorized COVID-19 vaccinations with Vaxzevria. Many safety and other concerns has encountered with this vaccine, which led some countries to restrict the use of this vaccine. Despite of this, WHO, EMA and MHRA continuing to recommend that benefits of the vaccine outweighing the risk of the occurrence of blood clots with low platelets.


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