active vaccination

Active immunisation (see also passive immunisation) is defined as the administration of the immunogen (vaccine) with the aim of establishing long-term effective protection against a pathogen or against its toxins.

Inactivated vaccines: contain killed pathogens.

Subunit and split vaccines: do not contain complete killed pathogens, but only biomolecules derived or genetically engineered from them. Most influenza vaccines are split vaccines.

Conjugate vaccines are subunit vaccines: with these, the pathogen molecule is not introduced directly into the vaccine, but is bound beforehand to proteins (conjugates), which represent a carrier substance.

Special form of the dead vaccines: toxoid vaccines (formalin-inactivated toxin = toxoid).

Live vaccines: contain attenuated pathogens weakened in their virulence.

Examples of live (L) and dead (T) vaccines:

• Cholera (T)
• TBE = early summer meningoencephalitis (T)
• 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) (L, T)
• Genital / anal cancers caused by human papillomavirus (HPV) (T)
• Japanese encephalitis (T)
• Pneumococcal pneumonia and otitis media (T)
• Pertussis (whooping cough) (T)
• Polio (T)
• Tetanus = tetanus (T)
• Rabies (T)
• Typhoid fever (L, T)
• Human papilloma virus (HPV) (T)

RNA vaccines: such as BNT162/BioNTech/Fosun/Pfizer and mRNA-1273/Moderna/NIAID, usually consist of single-stranded messenger ribonucleic acid(mRNA). This contains the genetic information for the assembly of a protein. In the cytosol, the mRNA is bound by ribosomes and a peptide is built. The RNA in vaccines is usually packaged in liposomes or lipid nanoparticles (LNP). Since the antigen is produced in the body's own cells and in large quantities, the immune response is usually strong.

DNA vaccines: consist of a piece of DNA inserted into bacterial plasmid. This encodes the antigen and is taken up into the target cell and read. A DNA vaccine under development at Corona is INO-4800 - Inovio Pharmaceuticals.

Vector virus vaccines: here the gene of the pathogen in question - e.g. the Ebola virus - is added to harmless viruses. Although these viruses can penetrate human cells and possibly multiply there, they do not lead to an outbreak of the disease. The infected cell then produces the pathogen antigen = antibodies based on the gene for a while.

For example, in active immunisation with live vaccines, attenuated pathogens, i.e. pathogens weakened in their virulence but still capable of reproducing but no longer capable of causing serious disease themselves, or even fragments of pathogens are administered. This leads to a subclinical infection that mimics the wild infection.

The organism responds to this subclinical infection by producing antibodies and memory cells. Building measurable and resilient immunity (basic immunization) takes at least 7-10 days.

Many active immunizations trigger lifelong immunity(varicella, rotavirus, BCG, yellow fever, typhoid). Other active immunizations must be refreshed at regular intervals. The individual vaccination dates are specified in the so-called "vaccination schedule". Such booster vaccinations thus serve as a renewed "reminder" of the immune system and maintain the vaccination protection.

The prerequisite, however, is that the vaccinated person (vaccinee) is immunocompetent. Active vaccination fails, for example, in the case of iatrogenic immunosuppression, hereditary immunodeficiencies, leukaemia or after an acute EBV or HIV infection. Also old people often do not react properly because of an immunosenescence.

1. Hof H (2019). Vaccinations. In: Hof H, Schlüter D, Dörries R, eds Duale Reihe Medizinische Mikrobiologie. 7th, completely revised and expanded edition. Stuttgart: Thieme p 738