Immunoprophylaxis of viral infections

General principles of combating viruses

For many years, medical practice has utilized two effective methods for combating viral infections. These methods encompass both the prevention and treatment of diseases. We are referring to active and passive immunization.

Both approaches share a common overarching goal: to prevent the virus from realizing its pathogenic potential in the human body. However, the ways to achieve this goal, the mechanisms of action of the drugs used, and the clinical situations in which they are prescribed differ fundamentally. The choice between active and passive immunization depends on whether we need to prepare the body for a potential encounter with an infection in the future, or whether immediate protection is required here and now, once contact with the pathogen has already occurred.

Active immunization: how vaccines work

Active immunization (vaccine prophylaxis) is based on the administration of specific antigens into the body. The immune system recognizes these antigens and triggers a cascade of reactions, resulting in the production of endogenous antibodies.

From a pharmacodynamic perspective, the key target for synthesized antibodies is specific viral envelope proteins. The mechanism of action is as follows: antibodies bind to these proteins and physically block the process of adsorption—the attachment of the virus to the host cell membrane. Since the virus is prevented from entering the cell, the infectious process is halted.

The main clinical goal of vaccination is routine prophylaxis, i.e., reliably preventing infection before contact with the pathogen. The spectrum of infections controlled in this manner includes measles, rubella, mumps, and hepatitis B.

Special attention should be paid to an exception to the general rule: the rabies vaccine. This is a unique example of the therapeutic and prophylactic use of active immunization. The drug is administered to the patient not before, but directly after infection (e.g., following an animal bite). The purpose of such administration is to timely induce immunity and prevent the development of the disease.

Passive immunization: ready-made protection

Passive immunization differs fundamentally from active immunization in that pre-formed antibodies are administered to the patient. The body does not spend time synthesizing them, which provides immediate protection. The primary tool here is immunoglobulin preparations.

The most widely used is normal human immunoglobulin. In its composition, this preparation is predominantly immunoglobulin G (IgG). Its mechanism of action aims to prevent the adsorption of viruses on the surface of susceptible cells. An important feature of the pharmacodynamics of normal immunoglobulin is that, in addition to specifically binding viruses, it exhibits a pronounced non-specific immunostimulatory effect.

This preparation is administered exclusively intramuscularly. Indications for its use are quite broad:

• Emergency prophylaxis. Used when contact with an infected individual has already occurred. Effective in cases of exposure to measles, hepatitis A, pertussis, influenza, and poliomyelitis.
• Prophylaxis of various bacterial and viral infections.
• Inclusion in complex therapy for the treatment of established infections.
• Use in immunosuppressed patients when their own immune system is incapable of mounting an adequate response.

Monoclonal antibody preparations

A modern trend in passive immunization is the use of monoclonal antibodies. Unlike normal human immunoglobulin, which contains a pool of various antibodies, monoclonal preparations possess absolute specificity for a single specific pathogen.

A prominent representative of this group is palivizumab (commercial name: Synagis). Its specificity is strictly limited: these are monoclonal antibodies directed exclusively against respiratory syncytial virus (RSV).

In clinical practice, palivizumab has a clear indication. It is used for the prophylaxis of RSV infections in pediatric patients who belong to the high-risk group for severe disease progression.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Mechanisms of viral adsorption on the host cell membrane
• Pharmacokinetics of intramuscular immunoglobulin administration
• Features of immunosuppression and indications for passive immunization
• Differences between monoclonal antibodies and normal human immunoglobulin
• Regimens for emergency prophylaxis of measles, hepatitis A, and poliomyelitis

Other topics in the "Antivirals" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.