How Vaccines Work

The vaccines act by stimulating the immune system to produce antibodies, which can fight infectious diseases, making the individual immune to them.

Syringe with vaccine
Syringe with vaccine
 


How immunizations work

The purpose of immunizations is to stimulate the body to produce antibodies against certain germs, especially bacteria and viruses. Our immune system creates specific antibodies whenever it comes in contact with a germ. If we come in contact with the rubella virus, for example, we get sick only once, because the body produces antibodies that prevent the virus from infecting us again in the future.

The logic of the vaccine is to try to stimulate the body to produce antibodies without it having to have become sick before. We try to present to the immune system the bacteria or virus so that there is antibody production, but there is no development of the disease.

Usually a vaccine works only against a single germ. For example, the measles vaccine does not protect the patient against chicken pox and vice versa. There are already joint vaccines, which are actually two or more vaccines given in a single administration, such as the triple viral vaccine, which is composed of three vaccines in a single injection: measles, rubella and mumps. The immune system is simultaneously stimulated against these three viruses. Not every vaccine can be given together.

Types of vaccines and immunizations

The great difficulty in developing a vaccine is to create it so that the bacteria or virus can stimulate the immune system to create antibodies but are not capable of causing disease. Sometimes it is enough to expose the organism to the dead bacterium or virus to produce antibodies and make the patient immune to this germ. However, not all dead viruses or bacteria are able to stimulate the immune system, so we have to find other solutions to immunize the patient.

The degree of maturity of the immune system is also important. Ideally, we could give all the vaccines to the baby soon. Unfortunately this does not work. Our immune system needs time to develop and be able to generate antibodies when stimulated by vaccination.

A. Inactivated vaccines


Inactivated vaccines are those made with dead germs or only parts of the germ. Dead germ vaccines are the safest but usually have a lower immunization capacity, requiring more than one dose to provide prolonged protection. In some cases the immunization disappears after a few years, requiring the application of booster doses.

Often it is not necessary to expose the immune system to any virus or bacteria. The germ can be grown in the laboratory and parts of its structure that are not needed to create antibodies can be removed. In some cases, a single protein in the germ is so different from our own proteins that it is enough for the immune system to recognize it as something foreign by producing efficient antibodies against the invader. Vaccines with subunits of germs usually have between 1 and 20 parts of the same.

Examples of vaccines with viruses or inactive bacteria:

Examples of vaccines with one or more parts of the germ:

B. Toxoids


Sometimes what causes disease is not the bacteria itself, but rather some toxins that it produces. In this case, the vaccine does not need to be directed against the bacteria, it is enough that the immune system can have antibodies against the toxins. Toxoids are vaccines made with modified toxins, incapable of causing disease.

The toxoids also usually generate a weak immunization, needing reinforcement after a few years.

Examples of vaccines with toxoids:
  • Tetanus
  • Diphtheria

C. Immunoglobulins


Immunoglobulins are a different type of immunization than vaccines. Vaccines are called active immunization because they induce the immune system to produce antibodies. Immunoglobulins are called passive immunization, since they themselves are already the antibodies.

When exposed to a particular germ, the immune system may take a few weeks to produce antibodies in adequate quantity to fight it. In some cases, the disease is so aggressive that we do not have time to wait for the production of these antibodies. Hence the need to use immunoglobulins, which are a collection of antibodies previously formed by other people or animals. We take antibodies already formed by others and administer to the patient, and there is an immediate fight against infection.

Immunoglobulins cause a short immunization, sufficient only to treat the infection. The patient is not immunized for a prolonged time, and administration of a vaccine after the disease is necessary. For example, a non-vaccinated hepatitis B health professional who accidentally punctures himself with an infected needle needs to take the immunoglobulin and the vaccine to avoid becoming infected. The immunoglobulin will prevent the current infection while the vaccine will serve in this particular case only to prevent it from future contamination.

Examples of diseases that can be treated with immunoglobulins (antibodies):
  • Hepatitis B
  • Anger
  • Botulism
  • Diphtheria
  • Tetanus
  • Chickenpox - varicella
  • Measles

D. Live attenuated virus vaccines


The ideal is always to create vaccines with dead germs, incapable of causing diseases. However, this is not always possible. There are cases in which we can not induce the production of antibodies by the immune system unless it is exposed to the living germ. In this case, the option is to keep the virus or bacteria alive but attenuated, that is, weak enough to fail to cause relevant symptoms.

Live germ vaccines are safe in healthy patients, but should not be given to people with deficiencies in the immune system, such as transplanted, AIDS patients, patients on immunosuppressive drugs, or patients on chemotherapy. This group is at high risk of developing the disease if they take the vaccine.

Pregnant women also can not take live virus vaccines because there are risks of infection of the fetus and complications of pregnancy. We will specifically talk about vaccination during pregnancy in a separate article, which will be written in the coming weeks.

Because live germ vaccines are the closest to actual infection, they are often the best stimulants for the production of antibodies by the immune system. This type of vaccine usually requires only one or two doses and produces an immunization for many years, sometimes for the rest of life.

Live attenuated virus vaccines are easier to produce than bacteria, which are much more complex germs and difficult to handle.

Examples of vaccines with live attenuated bacteria or virus:

Why are there no vaccines against HIV and other infections?

We can not always handle our immune system properly. There are several germs that are naturally less stimulating to our immune system. Some viruses quickly "hide" within points in our body, preventing the immune system from recognizing them.

In the case of the HIV vaccine there are some important points. The dead virus does not seem to be able to stimulate the immune system. On the other hand, vaccination with live virus is dangerous because it is not a benign infection, such as chicken pox or rubella. To have a live HIV vaccine it is necessary first to be sure that we will not infect the patient instead of helping him to create antibodies. We have to find a way to mitigate HIV so that it is incapable of causing disease but capable of inducing the creation of antibodies. Most searches today are not made with live HIV.

The way the HIV virus works also hampers the production of vaccines. The virus lurks within the cells of the immune system, making it difficult for the body to produce antibodies against it. In addition, HIV mutates very quickly, and the virus may have different proteins between two infected people. It is necessary to identify a protein that is common to all viruses and that also can stimulate the production of antibodies by the immune system.

Taking the same vaccine more than once does it harm?

Many people get confused when they lose the vaccination card because they are afraid of taking a vaccine that has been given in the past. There is no problem repeating vaccines. Many of them, moreover, need to be strengthened from time to time, such as tetanus, yellow fever and diphtheria vaccines, which lose their effect after 10 years.

If there is any doubt about prior immunization with a disease, it is best to vaccinate. If the patient has previously taken the vaccine, this will not hurt. It is worse to leave the patient unimmunized and exposed to infection.

The only precaution is to not administer the same vaccine at intervals of a few days, especially if it is a live vaccine because there is no increase in efficacy and the risk of side effects is very high.

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