Vaccines – how they work and what they protect against

Vaccines protect against infectious diseases by stimulating the immune system to produce antibodies and multiply certain immune cells. They are one of the most important means of prevention against diseases. Research-based pharmaceutical companies continue to develop new and improved vaccination options. A distinction is made between inactivated vaccines, live vaccines and gene-based vaccines.

An infant looks up while being inoculated with a syringe in the right upper arm

The human immune system can actually defend itself against many pathogens. Among other things, it produces antibodies and multiplies certain immune cells that specifically act against the invaded germ. These persist long after infection, creating a long-lasting protection, an immunity.

More on immune defenses and the effects of vaccination:
Active and passive immunization

But with some pathogens, the body has difficulty defending itself if it has never encountered this germ before. Vaccination means to make the immune system preventively familiar with the characteristics of a pathogen by means of vaccines, before a real infection occurs. The immune system reacts like in a real infection and creates immunity. In case of a later infection, the disease does not break out at all or at least takes a milder course. The pathogen components that cause the immune response are called antigens (from"Antibody generating"; not from "gene").

Vaccines are also called vaccines. The name is derived from vaccinus – latin for "from the cow – her. This is because fluids containing cowpox virus were used to effectively vaccinate against smallpox in England from 1796 onwards. "vaccinated", as it was called there. This was one of the first vaccination methods in history.

Active vaccinations: Prevention against infectious diseases with live, dead and gene-based vaccines

Doctors call the vaccinations also active vaccinations, because the human body must become active in reaction to the vaccination, in order to develop the desired immune protection. Live vaccines as well as inactivated vaccines can protect vaccinated persons for many years – sometimes even for life. However, this is often achieved only after they have been injected two or three times in succession at intervals of weeks or even months. However, there are also vaccinations for which an injection is sufficient. How long gene-based vaccines (vector virus vaccines, mRNA vaccines) protect remains to be seen; they have only been around for a comparatively short time.
All available vaccines are directed against infectious diseases. Cancers in the genital/anal area of women and men as well as genital warts are also included, as they are caused by different strains of sexually transmitted human papillomaviruses (HPV).

Today you can protect yourself from the following diseases with approved vaccines:

  • Cholera [T, L]
  • Covid-19 [M, V]
  • Dengue fever [V]
  • Diphtheria [T]
  • Ebola [V]
  • TBE = early summer meningoencephalitis [T]
  • Yellow fever [L]
  • Genital warts caused by human papillomavirus (HPV) [T])
  • Haemophilus influenzae b infection (Hib infection) [T]
  • Hepatitis A [T]
  • Hepatitis B [T]
  • Herpes zoster (shingles) [L, T]
  • Meningitis or sepsis caused by meningococci of serogroups A, B, C, W135, and Y [T]
  • Influenza (seasonal true flu) [T, L]
  • Japanese encephalitis [T]
  • Cancers in the genital / anal area caused by human papillomavirus (HPV) [T]
  • Pneumococcal pneumonia and otitis media [T]
  • Malaria [T] (only for small children in malaria areas)
  • measles [L]
  • Anthrax [T
  • Mumps [L]
  • Pertussis (whooping cough) [T]
  • Smallpox [L]
  • Polio [T]
  • Rotaviruses (vomiting diarrhea) [L]
  • Rubella [L]
  • Tetanus = Tetanus [T]
  • Rabies [T]
  • Typhoid [L, T]
  • Varicella (chickenpox) [L]

[L] and [T] stand for "live vaccine" and. "Dead vaccine", [V] stands for "vector virus vaccine" and [M] for "mRNA vaccine"

The only vaccine against tuberculosis, the so-called BCG vaccine, is not used in Germany because of its poor benefit-risk ratio in this country. In addition, it is ineffective in adults.

In addition to vaccines against individual diseases, there are also Combination vaccines, that protect against up to six diseases at the same time. This reduces the number of injections required compared to single vaccinations. Combination vaccines are used primarily for basic immunization of children and for booster vaccinations in adults.

Live vaccines often achieve particularly long protection

Live vaccines contain reproducible pathogens. But it concerns mostly strains of the pathogens, to which the ill-making characteristics were bred off. These are called "attenuated" pathogens. The live vaccines against mumps, measles and rubella contain such attenuated viruses and usually cause lifelong vaccination protection.

Attenuated viruses are associated with the residual risk that the vaccination may, in rare cases, cause symptoms similar to those caused by the disease itself. But the symptoms are usually very mild and last only a few days. Nevertheless, for this reason there are special recommendations of the Robert Koch Institute for pregnant women.

Inactivated vaccines

Inactivated vaccines contain only "dead", i.e. non-replicable, material: these are killed pathogens or components of them, the antigens (s.o.). The immune protection provided by inactivated vaccines usually only lasts for a few years and must then be replaced if necessary. are refreshed.

Specific forms of dead-enders include, in particular, the following:

Subunit and split vaccines: They do not contain whole killed pathogens, only biomolecules derived from them or genetically engineered. Most influenza vaccines are split vaccines, which are produced from real influenza viruses. Several subunit vaccines also contain selected molecules of a pathogen, but these were not derived from the pathogen itself but were produced by genetic engineering in large steel tanks using yeast, mammalian or insect cells. The necessary genes of the pathogen were transferred to the cells beforehand. This applies, for example, to the vaccines against hepatitis B or cholera.

conjugate vaccines are subunit vaccines, in which the pathogen molecules are not introduced directly into the vaccine, but are previously bound to proteins that represent a carrier substance. These so-called conjugates achieve a stronger immune response and longer lasting protection than antigen alone. Several vaccines against meningitis and pneumonia are among the conjugate vaccines; here the antigens are polysaccharides from the surface of bacteria.

VLP vaccines contain virus-like particles. This means that the antigens are not simply dissolved in the vaccine in a disorderly fashion, but have combined with other molecules to form small structures that look like viruses. In some cases, this ensures a better vaccination effect. Unlike viruses, however, VLP are not capable of reproduction. Examples of VLP vaccines include vaccines against diseases caused by human papillomaviruses (HPV).

Gene-based vaccines

In the case of live and dead vaccines, the attenuated pathogens or pathogen antigens are supplied to the body with the vaccine. Gene-based vaccines, on the other hand, require body cells to produce an antigen themselves after the appropriate gene has been applied to them with the vaccine. The principle of vector virus, mRNA and DNA vaccines.

For Vector virus vaccines a gene of the pathogen in question (z.B. the Ebola virus) harmless viruses with it. These can penetrate human cells and possibly multiply there, but they do not make people ill. The infected cell then produces the pathogen antigen for a time on the basis of the gene, which leads to an immune reaction in the vaccinated person. The genetic material of the infected cells is not changed in the process. Harmless vector viruses are, among others, the vaccine viruses from smallpox and measles vaccines, or monkey adenoviruses. The first vector virus vaccines were approved for dengue fever and Ebola. Two of the Covid-19 vaccines approved in the EU also contain vector viruses.

mRNA vaccines on the other hand, do not contain viruses, but only the relevant pathogen gene in the form of so-called messenger RNA. This is packed into small vesicles, the lipid nanoparticles, and injected as a vaccine. When the messenger RNA enters cells, they use it to produce the pathogen antigen, which in turn leads to an immune response. Again, the genetic material of the body’s cells is not changed, and antigen production ends again after a short time. To date, there are two approved mRNA vaccines – both against covid-19 – and many more are in development against various diseases.

DNA vaccines are similar to RNA vaccines, but contain the pathogen gene in question in the form of the hereditary substance DNA. So far, there are no approved DNA vaccines, but there are some in development against Covid-19. The most advanced project has reached phase II testing with volunteers.

Passive immunization: when it is too late for vaccination

If a person has already been infected with pathogens, it is usually too late for vaccination. An exception is rabies, where active vaccination immediately after infection almost always still preempts a disease outbreak.

If vaccination has been missed, some pathogens can still be transmitted after entry by a Passive immunization with a so-called Antiserum keep in check. This is in a way a "transplanted vaccination". In the past, passive immunizations were sometimes also called "passive vaccinations". This involves injecting the patient with immunoglobulins obtained from the blood fluid (serum) of vaccinated humans and rarely that of horses as well. Immunoglobulins are also known as antibodies. The injection solutions for passive immunization are also called antisera in reference to their origin.

Read more about how researchers are using genetic engineering in development and production:
What pharmaceutical researchers are working on

For some years now, there have been a type of "artificial antisera". One of the two preparations approved to date contains antibodies against the RSV virus, which are not obtained from blood serum but genetically engineered were. In the other – also genetically engineered – antibodies against the toxin of the bacterial intestinal germ Clostridium difficle contain. Other antibody-based passive immunizations against other viral or bacterial infections are in development.

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