The possible adverse effects of the AstraZeneca vaccine under the magnifying glass of experts

Vaccination remains a vital tool in the fight against SARS-CoV-2, demonstrating its effectiveness in reducing hospitalizations and deaths related to the virus (Illustrative Image Infobae)

In the last few hours, the pharmaceutical company AstraZeneca officially acknowledged before the British courts that its COVID-19 vaccine can trigger thrombosis with thrombocytopenia syndrome (TTS) in extremely rare cases.

The development emerged in the context of a class-action lawsuit in the United Kingdom, brought by individuals who claim to have suffered serious injuries as a result of receiving the vaccine, which was developed in collaboration with the University of Oxford.

It is clear, first of all, that vaccination has been and is a vital tool in the fight against SARS-CoV-2, especially in reducing hospitalizations and deaths related to the disease.

All in all, this is not the first time that AstraZeneca has addressed the issue of possible adverse effects of its vaccine. For example, in a study published In The Lancet magazine in 2021, company scientists pointed out the existence of very rare cases of TTS after application. The firm reiterates that, despite these extremely low risks, the benefits of vaccination far outweigh the possible side effects.

Adverse reactions such as fever, discomfort and local pain are common after vaccination, according to Dr. Daniela Hozbor from CONICET, although most disappear quickly (Illustrative Image Infobae)

The vaccine developed by AstraZeneca and the University of Oxford is based on the use of an adenovirus (specifically a chimpanzee common cold virus), which, modified, acts as a vehicle to carry the antigen and for the body to generate the immune response. without actually causing illness. In other words, it is a kind of “Trojan Horse.”

The vaccine showed, as reported in May 2021 to Public Health England (PHE), that two doses are between 85% and 90% effective against symptomatic disease, figure for which an analysis of the real data obtained in the deployment of the vaccine was cited.

Consulted by Infobae, Dr. Daniela Hozbor, principal researcher of CONICET at the VacSal Laboratory of the Institute of Biotechnology and Molecular Biology (IBBM) of the Faculty of Exact Sciences of the National University of La Plata, pointed out: “As in other vaccines, in In this case there are some common adverse reactions that disappear quickly such as fever, malaise, headache, dizziness, pain at the site where the injection was received or myalgia. It had also been reported that, in a rare case, an inflammation of the blood vessels in the skin could appear, which is a cutaneous vasculitis and appears as a rash on the skin with red spots. This vasculitis generally disappears on its own without treatment.”

According to Hozbor, “in any vaccine, the risk and benefit are always evaluated, even with important adverse reactions such as TTS, which had been reported to have a frequency of between 0.3 and 1 in every 100,000 administrations.” . In terms of what the COVID disease itself causes, it is much less, and that is why the benefit is much greater. The prevention provided by the AstraZeneca vaccine in terms of avoiding illness, severe illness and death is greater than this risk.”

Adverse events from vaccines can vary and be caused by allergic processes or individual reactions, according to infectologist Ricardo Teijeiro (Illustrative Image Infobae)

“All medications, including vaccines, can cause mild, moderate or severe adverse reactions. There is no substance that provides absolute safety, and the idea is that the appearance of these reactions is with less risk than benefit,” the researcher considered.

And he added: “The safety of vaccines is studied throughout their development and, if it is proven to be safe and effective, it is passed on to the population. Later, as there is a lot of diversity, you can find something that you didn’t see because, unlike giving, for example, 30 thousand doses in a clinical trial, now you are giving millions. That is why vaccines continue to be studied in the general population to verify and continue to maintain the safety profile.”

“Adverse reactions can vary and may be due to allergic processes to a component of the vaccine, or even associated with the same event of anxiety about the vaccination. In turn, the vaccine itself can trigger an effect such as the case of TTS,” said Hozbor.

For his part, in dialogue with Infobae, infectious disease specialist Ricardo Teijeiro, member of the Argentine Society of Infectious Diseases, explained: “Adverse events, unless they are known allergies to a vaccine product, are difficult to prevent or warn about. In general, they are produced by the individual’s reaction process to the vaccine. Each person responds individually, and in some cases these events such as thrombosis can occur, which has immunological characteristics specific to each of us.”

The thrombosis associated with the AstraZeneca vaccine is within the safety parameters of the vaccines, said Jorge Geffner (Getty)

“Other adverse events that may occur are inflammatory events, local pain and general discomfort due to the same inflammatory process that the vaccine produces. These effects are treated symptomatically, that is, the symptom is targeted, because if these effects occur due to the vaccine, they are self-limiting, unless it is something serious,” Teijeiro added.

Another professional consulted by Infobae was Jorge Geffner, professor of immunology at the UBA and researcher at CONICET. “Astrazeneca is a very safe and effective vaccine. Like all pharmacological treatments, there may be a very low rate of unwanted effects. If you look at the package insert of any medication you take, you will see that there are always side effects. Well, in this case, thrombosis was the effect, but it is within the safety parameters with which vaccines are approved, so it does not violate any safety regulations and nothing in particular was hidden either. This does not discourage the use of the vaccine because the beneficial effects are much more positive than these undesirable effects.”

“The mechanism underlying this thrombotic phenomenon that was observed in a tiny minority of patients is not clear,” Geffner added. It is known that the vaccine awakens an antibody response and it could be that the thrombotic effect is mediated by these same antibodies that, in addition to defending against the virus, recognize something in the platelets of this small proportion of patients and cause them to aggregate forming thrombi.”

“Astrazeneca, like the other vaccines that were applied at the time of the pandemic and continue to be applied now, are safe and effective, but not exempt like any medication or therapeutic procedure from some significant side effect in a very small proportion of people. treated,” considered the CONICET researcher.

WHO supports the safety and effectiveness of the AstraZeneca vaccine /REUTERS/Dado Ruvic/Illustration/File Photo/File Photo

In turn, the molecular virologist at the National University of Quilmes and CONICET researcher, Mario Lozano, told Infobae: “These adverse effects are generally related to an exaggerated response of a part of our immune system or our immune system. general defense against vaccine components. Many times, for example, the fever or muscle pain that occurs after vaccination comes from what we call an inflammatory reaction. The inflammatory reaction is a non-specific defense of the body that precedes the immune reaction.”

“The inflammatory reaction implies that the body reacts against any adversary that enters and is unknown, in a very generic way that increases the possibility that the blood capillaries release fluid and cells to attack that invader, which produces an inflammation. Like everything, this increases the local metabolism, also the temperature and produces fever. Those are the most common reactions. Cases of thrombosis have to do with a malfunction in some people of the coagulation system, platelets and the components of that coagulation system,” Lozano postulated.

At the same time he stressed: “Every treatment has some risk, from an operation to a treatment with an antibiotic or, in this case, a preventive treatment that would be the use of a vaccine. These risks are evaluated, the cause is seen and the possibilities of its appearance and a decision is made based on that to vaccinate or not.”

The process that could lead to the formation of clots after vaccination with AstraZeneca involves several intermediate steps, suggesting a complex and unusual mechanism (Illustrative Image Infobae)

It should be remembered that the World Health Organization (WHO), through its Global Advisory Committee on Vaccine Safety, public earlier an analysis of the Oxford/AstraZeneca ChAdOx1-S (recombinant) vaccine, as it was called in the report.

“A new type of very rare adverse event, known as thrombosis syndrome with thrombocytopenia, has been reported after administration of this vaccine. This syndrome involves rare and serious blood coagulation disorders associated with low platelet counts. In countries where SARS-CoV-2 transmission is currently recorded, the advantages of getting vaccinated far outweigh the risks, given the protection conferred by the vaccine against COVID-19,” the WHO experts postulated.

While they highlighted: “Very rarely, cases of Guillain-Barré syndrome (a rare disorder in which the body’s immune system attacks the nerves, according to Mayo Clinic) after vaccination. At the moment, the causal relationship with the vaccine cannot be confirmed or ruled out. “More rigorous studies must be carried out to properly evaluate the significance of these cases.”

According to these experts, “the AstraZeneca vaccine is safe and effective in protecting people from the extremely serious risks posed by COVID-19, including severe clinical illness, hospitalization and death.” “It is recommended to administer two doses of 0.5 ml each intramuscularly, separated by an interval of between 8 and 12 weeks,” the WHO stated.

The pharma company had already pointed out in a paper published in 2021 the possibility of this adverse effect in very rare cases (Europa Press)

And job presented in the scientific journal Science Advances in December 2021 had already indicated that the interaction between the adenovirus envelope used in the vaccine and a protein called platelet factor 4 (PF4), present in human blood, could cause a response in rare cases. wrong immune system.

In rare situations, the immune system could mistake PF4 for the virus and initiate the production of antibodies, which could bind to PF4, forming clumps that could result in blood clots, experts say.

The scientists explained how small amounts of the vaccine’s ChAdOx1 adenovirus could enter the bloodstream through microlesions in the capillaries caused by the injection. This could lead to binding between ChAdOx1 and PF4, potentially triggering clot formation.

It is essential to highlight that this process involves several intermediate steps before clots form, suggesting that the mechanism is not direct or inevitable, but rather results from a sequence of unfortunate and rare events.