July 13, 2022 at 5:37 p.m. EDT
The newest entry into the U.S. arsenal of coronavirus vaccines uses the oldest technology of the bunch.
The four vaccines authorized by the Food and Drug Administration all teach the body’s immune system to recognize and attack the virus that causes covid-19, but each type does it a little differently.
The first two vaccines, by Pfizer-BioNTech and Moderna, debuted the newesttechnology. Johnson & Johnson’s vaccine was created using a slightly more conventionalmethod. The most recent vaccine to be greenlighted was made by Novavax through a process commonly used since the 1980s.
What all four have in common
Vaccines imitate an infection, giving the immune system a sort of practice target so that it learns how to quickly recognize and defend against the real virus.
All four coronavirus vaccines available in the United States trigger the immune system with antigens, benign replicas of bits of the virus.
Each type of vaccine delivers a different antigen in a different way, but they all teach the immune system to recognize the proteins that make up the virus’s signature spikes. Those spikes are the keys that allow the coronavirus to unlock and infect cells.
Once the antigens are inthe body, the reaction is the same.
Specialized cells break the antigens down into a form the immune system can recognize, and they pass the information along to other cells that marshal infection-fighting troops.
Injected vaccine
INSIDE BODY
Antigen-presenting cells (APCs) consume the antigen from the vaccine or made from the instructions in the vaccine. They break down the spike protein antigen into pieces called peptides and present those to T-helper cells.
Antigen
Antigen-presenting cell (APC)
T-helper cells use peptides to teach the immune system to recognize the virus and activate immune cells to combat an infection should the virus enter the body.
Peptide
T-helper cell
Then two armies of white blood cells — B cells and killer T cells — prepare to attack.
B cells produce antibodies that attach to the coronavirus’s spikes, blocking the virus from latching onto and invading healthy cells.
Meanwhile, killer Ts recognize the antigen residue on infected cells and kill those cells. That stops the virus from using the cell’s machinery to replicate itself.
Novavax contains lab-grown spikes
The Novavax vaccine is called a subunit vaccine because it uses a portion of a virus to activate the immune system.
Scientists grow coronavirus spike proteinsin the cells of fall armyworm moths inside giant bioreactors.(Insect cells are particularly good at making complex proteins such as those that make up the spikes.)
They mix in a detergent to create a spike-covered soap bubble that looks like the coronavirus. They also add an ingredient called an adjuvant that revs up the immune system so it will respond more forcefully.
HOW PROTEIN SUBUNIT VACCINES ARE CREATED
Moth cells are used to generate the spike protein. An ingredient, called an adjuvant, from the soapbark tree is added.
HOW PROTEIN SUBUNIT VACCINES ALERT THE IMMUNE SYSTEM
Inside the body, the adjuvant helps activate immune cells. This allows a smaller dose of spike proteins to be effective.
Copies of spike protein consumed by APC cells
Copies of the spike protein are then used by the immune system to activate immune cells to recognize and stop the virus.
APC
Adjuvant helps increase immune cell activation
Subunit vaccines take longer to produce than the newer types. A handful of cases of heart inflammation occurred during the Novavax trials, although it is unclear whether the vaccine caused the inflammation.
But Novavax has advantages. It stays stable longer under typical refrigeration, does not contain ingredients used in other vaccines that trigger allergies, and may appeal to people who prefer an older, more familiar technology. Some flu, hepatitis B and shingles vaccines are subunit vaccines.
Pfizer-BioNTech and Moderna deliver blueprints in fat bubbles
A Novavax shot contains ready-made virus spikes; a Pfizer-BioNTech or Moderna shot contains instructions so the body can make spikes.
These shots are called mRNA vaccines because they contain messenger RNA,a strip of synthetic genetic materialthat matches the virus. It is delivered in a tiny fat bubble.
Once inside a healthy cell, the RNA generates replicas of the spike proteins.
HOW MRNA VACCINES ARE CREATED
A synthesized bit of genetic material from the virus is wrapped in a protective lipid bubble to keep it from disintegrating.
HOW MRNA VACCINES ALERT THE IMMUNE SYSTEM
Inside cells, the genetic material acts like instructions for making copies of spike proteins.
Copies of the spike protein are then used by the immune system to activate immune cells to recognize and stop the virus.
Pfizer-BioNTech’s and Moderna’s shots are the first mRNA vaccines approved for widespread use, but the cutting-edge technology had been in development and testing for years before the pandemic.
The mRNA coronavirus vaccines can be manufactured quickly, and most people tolerate them well with no more than mild, short-lived side effects. But they are not ideal for everyone.
Some people are allergic to an ingredient used to stabilize the mRNA vaccines. In rare cases, vaccine recipients — mostly younger men — can develop heart inflammation after being vaccinated. And some people have been hesitant to try a new technology.
J&J delivers instructions in a cold virus
The vaccine created by Johnson & Johnson also carries spike-making instructions, but it does it differently than the mRNA vaccines. As a “viral vector” vaccine, it delivers a gene into the body in a harmless, modified cold virus.
Inside healthy cells, the gene delivers codes for the spikes and the cell churns them out.
HOW NON-REPLICATING VIRAL VECTOR VACCINES ARE CREATED
A harmless adenovirus, engineered so that it cannot replicate, is used to ferry a gene from the coronavirus into cells.
Viral vector technology is not new, but only a handful of vaccines made from it have been approved for use in humans, including an Ebola vaccine.
Because some people developed a rare but life-threatening blood-clotting syndrome within a few weeks of getting the Johnson & Johnson vaccine, the FDA has limited its use to those who cannot or choose not to get one of the other vaccines.
None of the coronavirus vaccines are made with the very oldest technology, which uses weakened or dead versions of the entire virus. Two well-known examples of such vaccines are the ones for polio and for measles, mumps and rubella.
Sources: Centers for Disease Control and Prevention, National Institute of Allergy and Infectious Diseases, University of Nebraska Medical Center
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