by Laura Cuppini
Cases of vaccine-induced immune thrombotic thrombocytopenia occurred in people under 50 years of age (mostly women), within two weeks of vaccination
AstraZeneca announced Wednesday that it has begun a worldwide recall of its Covid-19 vaccine.
Why was the anti-Covid vaccine produced by AstraZeneca withdrawn?
The request to withdraw the viral vector vaccine was presented by the Anglo-Swedish multinational that produces it, AstraZeneca, to the European Union on March 5 and came into force on May 7. Vaxzevria can therefore no longer be used in Europe. In the coming months, presumably, the vaccine will also be withdrawn in the United Kingdom and other countries where it is currently authorized. «Considering the quantity of available and effective vaccines for the new variants of Covid-19, there was no longer demand for the Vaxzevria vaccine which consequently was no longer produced or distributed. Not foreseeing future demand, AstraZeneca has therefore decided to withdraw the marketing authorization” explained the company.
What characteristics does the Vaxzevria vaccine have?
It is a viral vector vaccine based on the ChAdOx1 adenovirus, developed at the Jenner Institute of the University of Oxford in collaboration with AstraZeneca and the Italian IRBM Science Park. It was approved in the United Kingdom on 30 December 2020. At the end of January 2021, Ema (European Medicines Agency) and then Aifa (Italian Medicines Agency) also gave the green light for administration in subjects aged 18 years or over. ChAdOx1 is a chimpanzee adenovirus (Chimpanzee Adenovirus Oxford 1), responsible for the common cold. To produce the vaccine, a weakened version of the adenovirus (incapable of replicating and harmless to the human body) was used, into which the genetic material of the Sars-CoV-2 Spike protein was inserted. Once the vaccine is administered, the adenovirus enters the nucleus of the cell where it provides the genetic code to produce the Spike protein. In this way, T cells activate the immune response and the production of specific antibodies against the virus. The Vaxzevria vaccine is administered in two doses, in the arm muscle: the second must be administered during the twelfth week and in any case at least ten weeks apart from the first.
What do we know about possible side effects?
In April 2021, the EMA Safety Committee (Pharmacovigilance Risk Assessment Committee, Prac) stated that the Vaxzevria vaccine can cause a very rare side effect: this is vaccine-induced immune thrombotic thrombocytopenia, Vitt ). Most reported cases occurred in people under 50 years of age (mostly women), within two weeks of vaccination. The Committee analyzed 62 episodes of cerebral venous sinus thrombosis and 24 of splanchnic vein thrombosis (in the abdomen) reported in the EU medicines safety database (EudraVigilance) as of 22 March 2021, 18 of which were fatal. The cases mainly came from European and UK spontaneous reporting systems, where around 25 million people had received the Vaxzevria vaccine.
Is the person who received it at risk?
According to the EMA, a plausible explanation for the combination of blood clots and low platelets is an immune response leading to a condition similar to that sometimes observed in patients treated with heparin (heparin-induced thrombocytopenia, Hit ). But, the EMA underlined in April 2021, «Covid-19 is associated with the risk of hospitalization and death. The combination of blood clots and low platelets is very rare and the overall benefits of the vaccine in preventing Covid-19 outweigh the risks of side effects.” Three years later, April 2024, in a legal proceeding in London, AstraZeneca admitted that the vaccine «may, in very rare cases, cause thrombosis syndrome with thrombocytopenia», underlining however that «according to independent estimates, only in the first year of use Over 6.5 million human lives have been saved from the Vaxzevria vaccine and over 3 billion doses have been supplied globally.” All reported cases of vaccine-induced immune thrombotic thrombocytopenia occurred within a few weeks of vaccination, so those who have received the AstraZeneca vaccine for several months or even years are now at no risk of developing it.
Does the problem of adverse events only concern the AstraZeneca vaccine?
No, it concerns all viral vector vaccines, therefore also the one produced by Johnson & Johnson/Janssen (Ad26.COV2.S). After the suspicion of a link with cases of thrombotic thrombocytopenia, between March and April 2021, the use of the vaccine produced by AstraZeneca was blocked by the health authorities of several European countries and its use was subsequently approved by the EMA following evaluation of the risk/benefit ratio. The data relating to adverse events associated with the Johnson & Johnson/Janssen vaccine have been evaluated by the US Food and Drug Administration (FDA) and the use of the vaccine has been approved under the emergency use authorization clause, in consideration of the severity of the ongoing pandemic. In April 2021, the New England Journal of Medicine reported the analysis of 39 cases of thrombosis, observed after the administration of the vaccine produced by AstraZeneca: they arose from 5 to 24 days after administration of the vaccine, were mainly localized in atypical locations and occurred in predominantly young subjects, without significant clinical history and without history of thromboembolic nature. In addition to those from AstraZeneca and Johnson & Johnson/Janssen, two other mRNA-based anti-Covid vaccines were developed and approved by EMA (and Aifa) between December 2020 and March 2021: BNT162B2 (Pfizer/BioNTech) and mRNA-1273 (Modern). Both are still in use around the world, with versions updated to new variants. mRNA vaccines have no association with the rare risk of thrombocytopenic thrombosis.
What happened in Italy?
After the first evidence of a possible association between the AstraZeneca vaccine and thrombocytopenic thrombosis, at the beginning of May 2021 the Covid Technical-Scientific Committee suggests reserving the administration of the vaccine to subjects aged 60 and over. Cases of thrombocytopenic thrombosis occurred mostly in people under 50, preferably women. Tragedy occurred on 10 June 2021: an 18-year-old girl from Genoa, Camilla Canepa, died 16 days after receiving the AstraZeneca vaccine during one of the open days organized by the Regions to vaccinate on a voluntary basis those who were not yet in the groups of citizens who age and clinical situation were vaccinated with priority. At that time there was a shortage of vaccines, especially mRNA, and hundreds of people were dying a day from Covid in Italy. In relation to the death of Camilla Canepa, five people are under investigation today.
May 8, 2024 (modified May 8, 2024 | 3:04 pm)
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