A cross-sectional study of seroprevalence in Armenia, 2025: measles, mumps, rubella, and diphtheria

Prevention and control of vaccine-preventable infections is a key component of maintaining public health, and the overall state of immunity is the determining factor.

To study herd immunity of the Armenian population to measles, rubella, mumps, and diphtheria.

The study involved 5,513 individuals from all regions aged from 1 year and above. A cohort of volunteers, stratified into 9 age groups, was formed including by region and activity using a web application. For each infection, the presence and/or levels of immunoglobulin G were determined by the enzyme immunoassay method using Russian-made test systems.

The cohort average seroprevalence values for measles, rubella, mumps, and diphtheria were 88.3%, 97.2, 83.2, and 56.3%, respectively. The least protected age groups were: children <5 years (80.7% seropositive) and adults 30-49 years (82-83%) regarding measles; adolescents and adults <49 years (73-79%) regarding mumps; and the older adults (34.4%) regarding diphtheria. Most volunteers had: low or moderate measles Ab levels (0.18-1 IU/mL); high levels of rubella Abs (>200 IU/mL); and a basic protective level of diphtheria toxin Abs (0.1-1 IU/mL). With age, a trend is seen: seropositivity for the viral pathogens (measles, mumps, and rubella) increased to maximum values; and diphtheria seropositivity decreased to minimum values.

The level of herd immunity in Armenia is sufficient only for rubella, as confirmed by the absence of cases. Currently, immunity to measles and mumps is present, which prevents outbreaks but may not be fully preventive of sporadic cases. Despite the absence of diphtheria, insufficient protection in older adults makes them a risk group for incidence and severity. However, immunity levels in our study were assessed based only on humoral immunity, which may underrepresent the full immunological response, including that mediated by cellular immunity.