What do we know about vaccines?
Vaccines are pharmaceutical preparations intended to produce immunity against a particular disease by causing the body to produce antibodies.
Antibodies are proteins produced by B lymphocytes (or B cells) of the immune system to recognize harmful substances called antigens. Antibodies circulate in the blood and are also known as gamma globulins.
Antigens are large molecules located on the surface of harmful microorganisms such as viruses, bacteria, fungi, and parasites. They can also be chemical compounds such as toxins, medications, and other foreign substances. The body recognizes the antigen as a foreign element.
When B lymphocytes encounter and recognize an antigen, they produce specific antibodies to destroy the harmful agent. Each antibody is unique to each antigen. The antibodies produced to attack a particular antigen remain in the blood, providing protection in the event that the body is attacked again by the harmful agent.
A vaccine is a strategy in which a dead or weakened infectious microorganism is inoculated so that the immune system reacts by generating antibodies and acquiring the memory to recognize and eliminate the infectious agent. Since their discovery, vaccines have provided a great benefit to humanity by preventing diseases that caused large epidemics and deaths.
There are several types of vaccines that use different strategies to teach the immune system to recognize and eliminate the harmful agent: inactivated vaccines, live attenuated vaccines, toxoid vaccines, and subunit, recombinant, polysaccharide, and combination vaccines. Recently, new types of vaccines, such as messenger RNA (mRNA) vaccines and recombinant vector vaccines, are being studied.
Inactivated vaccines use the microorganism that causes the disease. They do not provide very strong protection and generally require several doses. Live attenuated vaccines are made from a weakened microorganism, creating a strong immune response. Subunit, recombinant, polysaccharide, and conjugate vaccines are produced from specific parts of the infectious agent. These vaccines produce strong immunity but usually require booster doses. Toxoid vaccines are made with a toxin produced by the infectious microorganism. The immune response depends on the toxin rather than the microorganism, requiring booster shots.
Currently, several types of vaccines against SARS-CoV-2, the virus that causes the COVID-19 pandemic, have been developed and are being administered as an effective prophylactic strategy for control and prevention. The Sputnik V vaccine, developed at the Gamaleya Research Institute in Moscow and approved by the Ministry of Health of the Russian Federation on August 11, 2020, uses the common cold adenovirus, which is modified to carry the spike (S) glycoprotein that coats the coronavirus. This allows the immune system to recognize the coronavirus if it enters the body.
Messenger RNA (mRNA) vaccines are a new type of vaccine that teaches cells to produce a protein that triggers an immune response if the body is infected by the virus. SARS-CoV-2 is known to use its spike (S) protein to bind to ACE2 receptors on human cells and cause infection.
The process for producing mRNA vaccines against SARS-CoV-2 began with understanding the coronavirus genome and identifying the gene that codes for the S protein, the glycoprotein that covers the virus and binds to the cell receptor. Subsequently, mRNA was synthesized with instructions to produce the virus's S protein in human cells, but with a different conformation than that of the coronavirus. In other words, the synthetic mRNA causes human cells to produce a slightly modified version of the viral protein, thereby alerting the immune system.
When the vaccine is injected into the arm, the synthetic mRNA enters the cells and instructs them to produce a portion of the spike protein of the virus that causes COVID-19. The immune system recognizes this protein as a foreign agent and begins producing antibodies, just as it would in response to a SARS-CoV-2 infection. As a result, the body learns to protect itself against the virus.
Because mRNA is a highly unstable molecule that decomposes easily, SARS-CoV-2 vaccines require very low temperatures to remain stable for days before use. These vaccines raise concerns because mRNA can stimulate inflammatory processes and immune responses. However, the mRNA vaccine strategy has been studied for decades in preclinical and clinical trials for cancer treatment.