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By the term Immunization we mean the process of inducing immunity against a specific infectious disease, microbial or viral. It is extremely important as it constitutes the main defense mechanism of the human body and can be induced passively through the administration of preparations containing ready-made antibodies or actively by the administration of vaccines that stimulate the immune system to produce a prolonged cellular immune response. In Greece, vaccinations are carried out based on the National Vaccination Program for Children and Adolescents as formulated by the National Vaccination Committee.

Passive Immunization is therefore the administration of ready-made antibodies from a human (immunoglobulins) or animal (immune sera or antisera), which has been immunized for the purpose of temporary prophylaxis against a specific infectious agent. It can also occur naturally through the transplacental transfer of antibodies from the mother, offering valuable protection in the first 5 months of life.

Historically, the importance of both Active and Passive immunization had become clear over time in Medical research, with the result that from the end of the 19th century to the 20th century, leaps have been made in it and it is now an important part of everyday Medical practice.

For the purposes of Passive immunization, 4 main types of preparations are used:

1. Common γ-globulin

It is a preparation that results from obtaining antibodies from a plasma pool of approximately 1000 healthy donors and has many uses in Pediatrics, such as replacement therapy in patients with immunodeficiencies, in Kawasaki disease and Multisystem Inflammatory Syndrome after Covid-19 infection, in Idiopathic Thrombocytopenic Purpura but also after organ transplants.

2. Hyperimmune γ-globulins

They are preparations with a high titer of antibodies against a specific pathogenic microorganism and are used for prophylaxis and treatment after exposure to microorganisms such as Hepatitis B, tetanus, rabies, CMV and chickenpox.

3. Immune sera (antisera)

They are preparations of equine antibodies, such as antitoxins for diphtheria and botulism.

4. Monoclonal antibodies

They are preparations of antibodies that have been mass-produced against a single antigen and have application in malignant and autoimmune diseases. In addition, in Pediatric practice, the monoclonal antibody Palivizumab is widely used for the prevention of RSV bronchiolitis in premature infants and children with congenital heart disease.

Common and well-known applications of Passive Immunization methods include the prevention and treatment of diseases such as tetanus and rabies by administering anti-tetanus and anti-rabies immunoglobulin intramuscularly after trauma and animal bites, while ensuring the patient is fully vaccinated. In addition, the preventive administration of γ-globulin for diseases such as Hepatitis A and measles in case of travel to an endemic country, in case of insufficient vaccination coverage, as well as the administration of antisera in case of snake bites and the prevention of maternal sensitization to Rhesus incompatibility.

Special mention is made of natural passive immunization, which involves the transfer of antibodies to the fetus or newborn from the mother, which is vital for the defense of the newborn/infant in the first months of life. It takes place during intrauterine life by transplacental transfer of antibodies, but also through breastfeeding with colostrum (colostrum).