Cómo funciona la vacuna contra la COVID-19 de Oxford-AstraZeneca

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Cómo funciona la vacuna contra la COVID-19 de Oxford-AstraZeneca

Oxford University has partnered with Anglo-Swedish company AstraZeneca to develop and test a coronavirus vaccine called ChAdOx1 nCoV-19 or AZD1222. In clinical studies, the vaccine was found to be 82.4 percent effective when given two doses 12 weeks apart. Despite the uncertainty about the trial results, the UK approved the emergency vaccine in December, and India approved a version of the vaccine called it Covishield January 3rd.

A fragment of the coronavirus

The SARS-CoV-2 virus is filled with proteins that it uses to enter human cells. These proteins, called spikes, are tempting targets for potential vaccines and treatments.

Gene of

Protein from

the summit

Gene of

Protein from

the summit

The Oxford AstraZeneca vaccine relies on the virus' genetic instructions to build the spike protein. Unlike the Pfizer-BioNTech and Moderna vaccines, which store instructions in single-stranded or single-stranded RNA, the Oxford vaccine uses double-stranded DNA.

DNA within an adenovirus

The researchers added the coronavirus spike protein gene to another virus called adenovirus. Adenoviruses are common viruses that often cause colds or flu-like symptoms. The Oxford-AstraZeneca team used the modified version of a chimpanzee adenovirus known as ChAdOx1. It can penetrate cells but not replicate in them.

DNA inside

an adenovirus

DNA inside

an adenovirus

AZD1222 is the result of decades of research into adenovirus-based vaccines. The first was approved for general use in July: an Ebola vaccine from Johnson & Johnson. Advanced clinical trials for other diseases such as AIDS and Zika are ongoing.

The Oxford-AstraZeneca vaccine against COVID-19 is more resistant than the mRNA vaccines from Pfizer and Moderna. DNA is not as fragile as RNA, and the adenovirus' hard protein shell helps protect the genetic material it contains. As a result, the Oxford vaccine does not need to be frozen. The vaccine is expected to last at least six months when refrigerated at 2-8 ° C.

Cell entry

After the vaccine is injected into a person's arm, adenoviruses collide with cells and cling to proteins on their surface. The cell wraps the virus in a bubble and pulls it inside. Inside, the adenovirus escapes from the bladder and migrates to the nucleus, the chamber in which the cell's DNA is stored.

Enveloped virus

in a bubble

Enveloped virus

in a bubble

Enveloped virus

in a bubble

virus

packed in

a bubble

virus

packed in

a bubble

virus

packed in

a bubble

virus

wrapped up

in one

bladder

virus

wrapped up

in one

bladder

The adenovirus introduces its DNA into the nucleus. The adenovirus is designed so that it cannot make copies of itself, but the coronavirus spike protein gene can be read by the cell and copied into a molecule called messenger RNA or mRNA.

Spike protein construction

The mRNA leaves the nucleus and the cell's molecules read their sequence and begin assembling the spike proteins.

Combine three

Spike proteins

Fragments

of spikes

and proteins

The gifts

Fragments

top

Combine three

Spike proteins

Fragments

of spikes

and proteins

The gifts

Fragments

top

Combine three

Spike proteins

Fragments

of spikes

and proteins

The gifts

Fragments

top

Combine three

Spike proteins

Fragments

of spikes

and proteins

The gifts

Fragments

top

Combine three

Spike proteins

Fragments

of spikes

and proteins

The gifts

Fragments

top

Combine three

Spike proteins

Fragments

of spikes

and proteins

The gifts

Fragments

top

Combine three

Spike proteins

Fragments

of spikes

and proteins

The gifts

Fragments

top

Some of the spike proteins produced by the cell form spikes that migrate to the surface and spread their tips. The inoculated cells also separate into fragments some of the proteins that they present on their surface. The immune system can then recognize these protruding spikes and spike protein fragments.

Adenovirus also triggers the immune system by activating the cell's alarm systems. The cell sends out warning signals to activate nearby immune cells. By activating this alarm, the Oxford AstraZeneca vaccine makes the immune system more responsive to spike proteins.

Intruder detection

When a vaccinated cell dies, its remains contain many spike proteins and protein fragments that can later take up a type of immune cell called an antigen-presenting cell.

Remains of a

dead cell

CELL

MODERATOR

OF ANTIGENS

Digestion of

Proteins

The gifts

a fragment of

Spike protein

Remains of a

dead cell

CELL

MODERATOR

OF ANTIGENS

Digestion of

Proteins

The gifts

a fragment of

Spike protein

Remains of a

dead cell

CELL

MODERATOR

OF ANTIGENS

Digestion of

Proteins

The gifts

a fragment of

Spike protein

The cell has fragments of the spike protein on its surface. When other cells called helper T lymphocytes recognize these fragments, the helper T lymphocytes can sound the alarm and prompt other immune cells to fight infection.

Formation of antibodies

Other immune cells called B lymphocytes could collide with coronavirus spikes on the surface of vaccinated cells or with floating spike protein fragments. Some B lymphocytes may be able to adhere to the spike proteins. Later, when helper T lymphocytes activate these B lymphocytes, they begin to multiply and secrete antibodies that attack the spike protein.

protein

corresponding

on the surface

Activation of

B lymphocytes

protein

corresponding

on the surface

Activation of

B lymphocytes

protein

corresponding

on the surface

Activation of

B lymphocytes

protein

corresponding

on the surface

Activation of

B lymphocytes

protein

corresponding

on the surface

Activation of

B lymphocytes

protein

corresponding

on the surface

Activation of

B lymphocytes

Activation of

B lymphocytes

protein

corresponding

on the surface

Activation of

B lymphocytes

protein

corresponding

on the surface

Activation of

B lymphocytes

protein

corresponding

on the surface

Activation of

B lymphocytes

Corresponding proteins

on the surface

Activation of

B lymphocytes

Corresponding proteins

on the surface

Activation of

B lymphocytes

Corresponding proteins

on the surface

Stop the virus

Antibodies can attach to coronavirus spikes, marking the virus for destruction, and blocking infection by preventing the spikes from attaching to other cells.

Suppression of infected cells

Antigen presenting cells can also activate another type of immune cell called a cytotoxic (or suppressive) T lymphocyte to search for and destroy coronavirus infected cells that have spike protein fragments on their surface.

CELL

MODERATOR

OF ANTIGENS

Presentation of

a fragment of

Spike protein

LYMPHOCYTE T.

CYTOTOXIC

ACTIVATED

Begins to suppress

to the infected cell

CELL

MODERATOR

OF ANTIGENS

Presentation of

a fragment of

Spike protein

LYMPHOCYTE T.

CYTOTOXIC

ACTIVATED

Begins to suppress

to the infected cell

CELL

MODERATOR

OF ANTIGENS

Presentation of

a fragment of

Spike protein

LYMPHOCYTE T.

CYTOTOXIC

ACTIVATED

Begins to suppress

to the infected cell

CELL

MODERATOR

OF ANTIGENS

Presentation of

a fragment of

Spike protein

LYMPHOCYTE T.

CYTOTOXIC

ACTIVATED

Begins to suppress

to the infected cell

CELL

MODERATOR

OF ANTIGENS

Presentation of

a fragment of

Spike protein

LYMPHOCYTE T.

CYTOTOXIC

ACTIVATED

Begins to suppress

to the infected cell

CELL

MODERATOR

OF ANTIGENS

Presentation of

a fragment of

Spike protein

LYMPHOCYTE T.

CYTOTOXIC

ACTIVATED

Begins to suppress

to the infected cell

CELL

MODERATOR

OF ANTIGENS

Presentation of

a fragment of

Spike protein

LYMPHOCYTE T.

CYTOTOXIC

ACTIVATED

Begins to suppress

to the infected cell

CELL

MODERATOR

OF ANTIGENS

Presentation of

a fragment of

Spike protein

LYMPHOCYTE T.

CYTOTOXIC

ACTIVATED

Begins to suppress

to the infected cell

CELL

MODERATOR

OF ANTIGENS

Presentation of

a fragment of

Spike protein

LYMPHOCYTE T.

CYTOTOXIC

ACTIVATED

Begins to suppress

to the infected cell

CELL

MODERATOR

OF ANTIGENS

Presentation of

a fragment of

Spike protein

LYMPHOCYTE T.

CYTOTOXIC

ACTIVATED

Begins to suppress

to the infected cell

CELL

MODERATOR

OF ANTIGENS

Presentation of

a fragment of

Spike protein

LYMPHOCYTE T.

CYTOTOXIC

ACTIVATED

Begins to suppress

to the infected cell

CELL

MODERATOR

OF ANTIGENS

Presentation of

a fragment of

Spike protein

LYMPHOCYTE T.

CYTOTOXIC

ACTIVATED

Begins to suppress

to the infected cell

Virus store

The Oxford AstraZeneca vaccine takes two doses four weeks apart to prepare the immune system to fight the coronavirus. During the clinical trial of the vaccine, the researchers accidentally only gave some volunteers half the dose.

Surprisingly, the vaccine combination, where the first dose was only half the second dose, was 90 percent effective in preventing COVID-19 in the clinical trial. In contrast, the combination of two full doses was only 62 percent effective. The researchers speculate that the first, lower dose better mimics the experience of infection and promotes a stronger immune response when the second dose is given.

Second dose

28 days

then

Second dose

28 days later

Second dose

28 days later

Because the vaccine is so new, researchers don't know how long its protection could last. Antibody and cytotoxic T lymphocyte counts may decrease in the months following inoculation. However, the immune system also contains special cells called memory B and T cells that can hold information about the coronavirus for years or even decades.

For more information on the vaccine, see AstraZeneca's Covid Vaccine: What You Need To Know.


Sources: National Center for Information on Biotechnology; Nature; Lynda Coughlan, University of Maryland Medical School.

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