Active Immunization – Vaccination and Immunity
Active immunization is a preventive measure in which a vaccine stimulates the immune system to produce its own antibodies, providing long-term protection against infectious diseases.
Things worth knowing about "Active Immunization"
Active immunization is a preventive measure in which a vaccine stimulates the immune system to produce its own antibodies, providing long-term protection against infectious diseases.
What is Active Immunization?
Active immunization is a form of vaccination in which the body is given a vaccine that stimulates the immune system to produce its own antibodies and memory cells. Unlike passive immunization, where ready-made antibodies are introduced from an external source, active immunization enables the body to build its own protective response. This self-generated immunity typically lasts much longer and can in some cases provide lifelong protection.
Mechanism of Action
During active immunization, the immune system is exposed to an antigen – a component or weakened form of a pathogen. The immune system recognizes this antigen as foreign and initiates an immune response:
- Specific B lymphocytes are activated to produce antibodies.
- T lymphocytes are generated that can recognize and destroy infected cells.
- A portion of activated immune cells develop into memory cells, enabling a rapid and effective response upon future exposure to the same pathogen.
This process is known as immunological memory and forms the basis for the long-lasting protection offered by active immunization.
Types of Vaccines
Several types of vaccines are used for active immunization:
- Live attenuated vaccines: Contain weakened but still replicating pathogens (e.g., measles-mumps-rubella, varicella).
- Inactivated vaccines: Contain killed pathogens or pathogen components (e.g., influenza, hepatitis A).
- Toxoid vaccines: Contain inactivated bacterial toxins (e.g., tetanus, diphtheria).
- Subunit vaccines: Contain specific proteins from the pathogen (e.g., hepatitis B, pertussis component).
- mRNA vaccines: Provide genetic instructions that direct the body to produce a specific antigen (e.g., COVID-19 vaccines by BioNTech/Pfizer and Moderna).
- Vector vaccines: Use a harmless carrier virus to deliver genetic information from the target pathogen into the body (e.g., certain COVID-19 vaccines).
Indications and Applications
Active immunization is used for both primary vaccination series in childhood and booster doses in adulthood. Health authorities such as the World Health Organization (WHO) and national bodies like the Standing Committee on Vaccination (STIKO) in Germany regularly publish vaccination recommendations. Key areas of application include:
- Childhood diseases (measles, mumps, rubella, chickenpox)
- Respiratory infections (influenza, pneumococcal disease, COVID-19)
- Liver infections (hepatitis A and B)
- Wound infections (tetanus, diphtheria)
- Travel vaccines (typhoid, yellow fever, meningococcal disease)
- Cancer prevention (human papillomavirus / HPV)
Primary Series and Booster Doses
Many vaccines require a primary vaccination series consisting of multiple doses to establish adequate immunity. Depending on the vaccine and the individual immune response, regular booster doses may be necessary to maintain protection over time. For example, tetanus protection is typically renewed every 10 years.
Side Effects and Risks
Active immunization is generally well tolerated. Common, usually mild reactions include:
- Redness, swelling, or pain at the injection site
- Low-grade fever or general malaise
- Fatigue and headache
Serious adverse events are very rare. Patients with known allergies to vaccine components (e.g., egg protein) should inform their healthcare provider before vaccination. Live attenuated vaccines are contraindicated in individuals with severely compromised immune systems, such as those undergoing chemotherapy.
Herd Immunity
A further goal of active immunization is achieving herd immunity: when a sufficiently large proportion of the population is vaccinated, pathogens can no longer spread efficiently. This also protects those who cannot be vaccinated themselves, such as newborns or immunocompromised individuals. The required vaccination coverage varies by pathogen – for measles, for example, approximately 95% of the population must be immune to prevent outbreaks.
References
- World Health Organization (WHO): Immunization. Available at: https://www.who.int/health-topics/vaccines-and-immunization
- Centers for Disease Control and Prevention (CDC): Principles of Vaccination. Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book), 14th edition. Available at: https://www.cdc.gov/pinkbook
- Siegrist, C.-A. (2018): Vaccine Immunology. In: Plotkin's Vaccines, 7th edition. Elsevier, Philadelphia.
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