RNA Vaccines

Specific prophylaxis of rubella

The rubella virus is an RNA-containing pathogen of the genus Rubivirus (family Togaviridae). It exhibits a pronounced affinity for embryonic, lymphoid, nervous, and epithelial tissues. The antigenic structure of the virus is stable—only a single serovar exists in nature. It is precisely this property that makes specific prophylaxis (vaccination) extremely effective.

The main epidemiological hazard of the infection lies in its effect on pregnant women. Mass outbreaks lead to severe consequences: multiple fetal malformations, stillbirths, and miscarriages (a historical example is the large-scale epidemic in the USA in the 1960s). Due to the high teratogenic threat, mandatory vaccination was introduced in many countries, including the Russian Federation.

Epidemiology and immunity features:

• Source: a sick person or asymptomatic carrier.
• Transmission: aerosol mechanism (airborne droplet route requiring close contact) for the acquired form and vertical (transplacental) for the congenital form.
• Susceptibility: the contagiousness index is about 80%.
• Immunity: persistent, lifelong immunity is formed after the infection. Infants under 6 months of age are protected by passive maternal antibodies (IgG).

Mumps vaccination

The pathogen of mumps infection is also an RNA-containing virus, but it belongs to the family Paramyxoviridae. As with rubella, its antigenic structure is characterized by high stability and is represented by a single serovar. This is a key factor ensuring the efficacy of applied vaccines.

The virus exhibits a pronounced tissue tropism. Target organs are glandular tissues (parotid, submandibular, salivary, sex, mammary, and pancreas), as well as the nervous system (with the risk of developing meningitis and meningoencephalitis).

Epidemiological nuances:

• Transmission: airborne droplet route. Close contact (less than 2 meters) is required, since the patient lacks catarrhal symptoms (cough, sneezing) and has reduced salivation, which hinders aerosol formation.
• Contagiousness: the peak of infectivity occurs in the first 3–5 days of the disease. The contagiousness index is 70%, and general susceptibility is 85%.
• Risk groups: predominantly preschool and early school-age children. Adults over 40 years old rarely fall ill due to the formation of an immune layer in the population.

RNA viruses without specific prophylaxis: Hepatitis C and D

Unlike rubella and mumps, not all RNA-containing viruses can be controlled using vaccines.

Acute viral hepatitis C Characterized by the complete absence of vaccines. Emphasis is placed exclusively on nonspecific measures: compliance with the sanitary and epidemiological regime and control of blood products. The infection poses a huge problem due to the high risk of chronic progression (70–80% of cases), in which persistence of viral RNA leads to liver cirrhosis and hepatocellular carcinoma. A two-stage approach is used for diagnosis:

1. Screening: detection of antibodies (anti-HCV) by ELISA.
2. Confirmation: detection of viral RNA by PCR (allows active infection to be distinguished from past infection).

Acute viral hepatitis D (delta hepatitis) Caused by an RNA-containing virus of the genus Deltavirus (family Togaviridae). Its key feature is obligate defectiveness. The virus is incapable of independent replication: to build its outer envelope (supercapsid), it absolutely requires the surface antigen of the hepatitis B virus (HBsAg). Consequently, delta virus monoinfection is impossible in principle, and the disease develops exclusively in individuals who are HBsAg-positive.

Class and exam questions

What else to study on this topic

• Mechanisms of transmission and pathogenesis of acquired rubella
• Dynamics of contagiousness in mumps
• Two-stage laboratory diagnosis of viral hepatitis C
• Variants of the clinical course of hepatitis D (features of coinfection)
• Anti-epidemic measures in rubella foci

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