Why Brazil stopped recommending the use of the AstraZeneca and Janssen vaccines against Covid-19

Published on 05/08/2024 09:28

The Ministry of Health no longer recommends the use of viral vector vaccines (AstraZeneca and Janssen) as a booster against Covid-19.

Viral vector vaccines are created from a type of adenovirus that does not harm human health.

Inside it, scientists insert some Sars-CoV-2 genes, causing the immunity of those who received the dose to be trained against the cause of Covid-19 without receiving the damage from the infection.

Anyone who has taken any of the vaccines, however — whether as a first dose or a booster — should not worry.

The interruption of the use and production of the vaccine by the Ministry of Health has nothing to do with effectiveness, but rather with a possible increased risk of thrombosis days after vaccination, according to a document published by the Ministry of Health.

The Ministry of Health informs that, until September 17, 2022, 98 cases (0.02 cases per 100 thousand doses applied) were reported on e-SUS — excluding data from São Paulo, which were not disclosed in the document suspicion of Thrombosis Syndrome with Thrombocytopenia (drop in platelets) with a temporal relationship to vaccines.

Of these cases, according to the agency, 34 were attributed to viral vector vaccines, 17 cases were recorded as having a probable relationship and 47 occurrences were considered possible cases.

The conditions, which were more common in women, occurred within a maximum period of 30 days after application. Those who received the dose longer ago and did not develop thrombosis are not considered to be at risk related to the vaccine.

BBC News Brasil asked the pharmaceutical companies AstraZeneca and Janssen for a position, which indicated that they had received the request, but did not send a response at the time of this publication.

WHY COULD VIRAL VECTOR VACCINES CAUSE THROMBOSIS?

“There is a possibility that some people — and we cannot identify this individually — have a very personal genetic characteristic, which, in contact with these viral vector vaccines, favors hypercoagulability, favoring the creation of thrombi”, explains infectious disease specialist Evaldo Stanislau de Araújo, from the Hospital das Clínicas of São Paulo.

According to the document from the Ministry of Health, “due to the rarity of occurrences, it has not yet been possible to identify risk factors associated with the syndrome, with the exception of an apparent increase in risk in individuals under 40 years of age”.

In the assessment of immunologist Gustavo Cabral, it is not possible to say with confidence, precisely due to the lack of clarity in the association, that vaccines are responsible for cases of thrombosis.

“The scientific studies I have read are very good, but there is a lack of explanation as to how the vaccine will be the trigger”, points out he, who is a researcher at the University of São Paulo and Fapesp (Fundação de Amparo à Pesquisa do Estado de São Paulo). ).

Despite the lack of detailed explanation, Cabral understands that the Ministry of Health’s decision is reasonable at the current epidemiological moment, in which viral vector vaccines are not indispensable as they were at the height of the pandemic.

VIRAL VECTOR VACCINE FULFILLED ITS ROLE AT A CRITICAL TIME

Among the possible consequences of a Covid-19 infection is precisely the creation of thrombi — with an incidence that is even much higher than the correlation made with viral vector vaccines.

A study published in the scientific journal Radiology shows that, among 3,342 people infected with Covid-19 who required hospitalization, the thrombosis rate was 16.5%.

“In 2021, when the possibility of these vaccines causing thrombotic conditions emerged, we were at a time of little supply of immunization agents and faced with a disease that is characterized by causing thrombosis. Failing to vaccinate with a vaccine that would hypothetically cause the condition would not have been correct at the time”, assesses the infectious disease specialist.

“This reasoning, in 2023, is no longer valid. The benefit of the vaccine today is inferior and it is unacceptable to pose a thrombotic risk. A large part of the population is vaccinated with multiple doses, meaning we have a protected population and a greater supply of vaccines. It is not reasonable to make the same analysis.”

CURRENT RECOMMENDATIONS

The production of AstraZeneca vaccine serum by Fiocruz, which had an agreement to produce a nationalized version of the vaccine, was interrupted.

The majority of patients were under 40 years of age, hence the official recommendation presented in the document for viral vector vaccines.

Cabral also draws attention to the fact that, after an initial dose of a viral vector vaccine, it is best to use another type of technology for reinforcement.

“These viral vector vaccines carry information from the virus to our cells. In subsequent doses, this information arrives in a less effective way.”

WHAT THRUMS ARE AND WHY THEY ARE DANGEROUS

Thrombi are blood clots formed in veins or arteries that hinder blood circulation and can appear in different parts of the body.

Depending on the location and size, clots can be considered more dangerous. In the lungs or brain, for example, they can block vital blood flow and lead to permanent damage and even death.

The report text points out that the most frequently reported clinical form was cerebral venous thrombosis. There are also reports of thrombosis of intrabdominal veins, pulmonary thromboembolism and arterial thrombosis.

[Folha Uol]