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With the emergency authorization for the Johnson & Johnson (J&J) coronavirus vaccine from the European Union and then from the Italian Medicines Agency (AIFA), a fourth solution has been added to combat the pandemic beyond those already available in Pfizer-BioNTech, Modern. and AstraZeneca. The vaccine was authorized following the recommendation of the European Medicines Agency (EMA) and should allow to accelerate the vaccination campaign in Europe because it requires the administration of a single dose, unlike other vaccines authorized so far that require two to a few weeks Standby. .
The J&J vaccine has already been used for a few weeks in the United States, where it was authorized on February 27, following the disclosure by the pharmacist of the first results of its clinical tests, carried out in several countries. The vaccine was 72 percent effective in the United States, while in South Africa it stopped at 64 percent, likely due to the circulation in the country of a variant believed to be more contagious. However, the vaccine is highly effective, almost entirely, in preventing severe cases of COVID-19 that require hospitalization.
In recent months, the European Union had contracted the supply of at least 200 million doses, starting in the second quarter of this year. Therefore, the first deliveries should take place between the end of March and the beginning of April, but it is likely that it will not be fully operational immediately, as it has emerged in recent days.
Adenovirus
The vaccine was developed by Janssen Pharmaceutica (owned by J&J) in collaboration with Beth Israel Deaconess Medical Center (United States). Unlike those of Pfizer-BioNTech and Moderna, based on messenger RNA, the J&J vaccine uses a virus (Adenovirus 26, or Ad26) that is essentially harmless to our body: in general, adenoviruses cause mild symptoms, similar to colds .
Researchers have modified it so that it can enter our cells, but without replicating or causing disease. Inside Ad26 they have also inserted the genetic material with the instructions to produce the protein spike that the coronavirus uses to bind to cells and replicate, carrying out the infection. These proteins are what form the coronavirus corona, as they appear to us under the microscope.
Stylized version of the coronavirus, its surface shows the peaks that contain the peak proteins that manage to bind to the cells of our body; the black line shows the genetic material (RNA) that the coronavirus then injects into the cell to replicate (Wikimedia)
In the cells
When the vaccine is injected, the modified Ad26 binds to certain types of cells by exploiting proteins on their surface. Once inside, they reach the cell nucleus and inject their DNA into it, which contains instructions for making the coronavirus spike protein. The information is read by the cell and copied into a molecule: messenger RNA (mRNA).
The mRNA moves away from the nucleus and is intercepted by other cellular structures (ribosomes) that use its instructions to build spike proteins. In practice, the vaccine makes the cells involved act like mini factories to produce just this particular piece of the coronavirus. The newly produced proteins reach the surface of the cell and do not go unnoticed by the immune system, which notices their unexpected presence.
Immune reaction
The mere presence of adenovirus causes our body’s defenses to be activated. This process, along with several others, helps increase the immune system’s reaction when it encounters spike proteins.
At the end of its life cycle, the cell that was induced to produce these proteins dies and its fragments are eliminated by other cells that specialize in cleaning. It is at this stage that spike proteins can come into contact with an “antigen-presenting cell” (APC), a type of immune system cell that displays antigens (foreign bodies) on its surface to enhance their presence.
This exposure is noticed by T helper lymphocytes, cells that keep substances in our body under control and that when they notice something strange they alert other immune cells to intervene.
Antibodies
Other cells of the immune system, B lymphocytes, found in circulation in the body, accidentally end up in contact with the cells that received the adenovirus and then produced the spike proteins. B lymphocytes bind to the latter, but they don’t have much idea what to do. They are activated when they meet helper T lymphocytes in their path, which sound the alarm, prompting them to multiply and produce antibodies to counter the protein.
A large number of antibodies are produced that remain in circulation in our body. In the event you come into contact with the actual coronavirus, the immune system has the tools to recognize the protein at its dangerous tips. Antibodies bind to these to prevent them from coming into contact with cell membranes, evading their defenses.
Destruction
Helper T lymphocytes are quite alert spies and also sound the alarm for another type of immune cell, cytotoxic T lymphocytes, which are activated to destroy any cell that shows it has the coronavirus protein on its surface, an indication of being infected. .
Immunity
The combination of helper T lymphocytes, B lymphocytes, cytotoxic T lymphocytes, and many other defense mechanisms can only work if the immune system has learned to recognize the coronavirus protein. The vaccine does just that: it educates our immune system, without having to learn these things the hard and dangerous way with the real coronavirus.
To date, we do not know how long the immune system keeps a memory of what it learns through vaccination, simply because current coronavirus vaccines have been used for such a short time. However, the first data are encouraging and in a few months we will have more detailed ones, derived both from the progress of clinical tests and the use of vaccines in the population.
Less delicate
The J&J vaccine is administered in a single dose and requires fewer precautions in storage than those with mRNA which must be kept at temperatures around -70 ° C. This is partly due to the need to keep mRNA molecules stable, which tend to to degrade easily. Instead, the genetic instructions for the J&J vaccine are kept inside the modified adenovirus, where they can stay longer, so it is sufficient to store the doses at refrigerator temperature.
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