Mongolia has been accelerating efforts to eliminate rubella. The combined measles–mumps–rubella (MMR) vaccine was introduced in 2009, leading to a steady decline in rubella incidence from 240 cases in 2012 to just 10 in 2022. However, rubella cases temporarily increased in Mongolia from 2015–2016, raising concerns about congenital rubella syndrome and coinciding with measles outbreak. This underscored the need to strengthen CRS surveillance, which plays a critical role in early case detection, guiding timely interventions, and informing immunization strategies.
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A health worker swabs alcohol on a young girl's arm to prepare for vaccination. Photo: WHO Mongolia
Why it is important to identify hidden burden of Congenital Rubella Syndrome?
Rubella is a highly contagious disease caused by a virus. It spreads easily when an infected person coughs or sneezes. When a woman is infected with the rubella virus early in pregnancy, she has a 90% chance of passing the virus on to her fetus. Rubella in pregnancy, especially during the first trimester, can result in miscarriage, fetal death, stillbirth, or infants with congenital malformations, known as congenital rubella syndrome (CRS).
Rubella remains a major public health concern. Globally, more than 1 500 CRS cases were reported in 2023, showing an upward trend. Identifying the hidden burden of CRS is crucial to understand the true scope of rubella’s impact, to recognize and address a preventable cause of lifelong disability, ultimately strengthen immunization programs, and protect future generations through effective prevention and care.
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Dr Socorro Escalante, WHO Representative to Mongolia and Dr Anauzaya Purevdagva, Technical Officer, WHO Mongolia, during the Congenital Rubella Syndrome Retrospective Review Training from 10-11 May 2025. Photo: WHO Mongolia
Looking back to move forward
While rubella surveillance is in place, CRS has not been systematically documented in Mongolia. To align with the Regional strategy and plan of action for measles and rubella elimination in the Western Pacific, Mongolia prioritized CRS surveillance under its National Action Plan for Infectious Diseases 2022–2025. Therefore, establishing evidence on CRS prevalence became essential to guide policy, improve child health, and achieve elimination targets.
In this context, WHO and the government conducted a national CRS study retrospectively by reviewing past hospital records to examine the hidden burden of CRS and, at the same time, to generate forward-looking evidence needed to shape future surveillance and policy.
The study aimed to identify the incidence and prevalence of CRS in Mongolia through retrospective hospital record reviews, while also establishing baseline evidence to support the development of a hospital-based monitoring system. In addition, the research sought to provide critical data for verifying Mongolia’s progress toward rubella and CRS control as part of the 2025 elimination goal.
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Group photos from the Congenital Rubella Syndrome Retrospective Review Training from 10-11 May 2025. Photo: WHO Mongolia
The study was carried out at the National Center for Maternal and Child Health, specialized private hospital for hearing “EMJJ” and regional diagnostic and treatment centers in the Uvurkhangai, Orkhon, Dornod, Khovd, and Umnugovi provinces. It focused on children under one year of age who had been admitted between 2015 and 2022. Researchers looked for cases that showed evidence of congenital rubella syndrome, including official discharge codes, positive rubella laboratory results, and clinical signs such as congenital heart disease, cataracts, or hearing impairment.
The medical records of 1 917 children were reviewed. The WHO case definitions for confirmed and probable cases were used as inclusion criteria. To avoid misdiagnosis and to improve the specificity and accuracy of case classifications, premature and low-birth-weight infants, as well as children who were not Mongolian citizens, were excluded from the review. To estimate the national burden, applied statistical analysis was employed.
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Data collection during the retrospective where medical records of 1917 children were reviewed for specific inclusion criteria. Photo: WHO/Mongolia.
Results
The review revealed a total of 63 confirmed and 557 probable cases of congenital rubella syndrome across the study sites. The most frequently observed conditions were congenital heart disease, cataracts, and hearing impairment—findings that mirror global patterns of CRS. When extrapolated to the national level, the estimated burden ranged between 2 080 and 3 250 cases over the period 2015–2022. These results contribute to the evidence that congenital anomalies, including those caused by rubella infection, remain a major factor in infant morbidity and mortality in Mongolia. The study presents a basis for strengthening CRS surveillance and improving national strategies for elimination.
Building a foundation for elimination
This is the first national study in Mongolia to quantify the prevalence of congenital rubella syndrome, providing much-needed evidence on a previously hidden burden. The findings point to the urgent need to establish hospital-based CRS surveillance and to integrate monitoring into the broader measles and rubella elimination strategies already underway. They also reinforce the importance of ensuring rubella immunity among women of reproductive age to prevent severe and irreversible birth outcomes. By generating both scientific data and policy direction, the study offers a strong foundation for strengthening immunization and surveillance systems in Mongolia.
The road ahead
Drawing from the evidence generated, Mongolia is on a clear path forward. The Government of Mongolia and the Ministry of Health have prioritized developing and institutionalizing a nationwide, hospital-based CRS surveillance system, with plans to launch it in 2026–2027. The study results will guide supplementary immunization activities and targeted efforts to ensure that women of reproductive age have high levels of rubella immunity. Sharing these findings through national and international publications will contribute to global CRS elimination efforts and highlight Mongolia’s leadership in advancing this important agenda.
Closing the gap on a hidden threat
By documenting the burden of congenital rubella syndrome for the first time and laying the groundwork for establishing a nationwide CRS surveillance system in 2026–2027, Mongolia has taken an important step in protecting mothers and children from preventable disability and death. This pioneering effort not only fills a critical evidence gap but also reaffirms the country’s commitment to achieving measles and rubella elimination. The study reflects the strong leadership of the Government of Mongolia, the Ministry of Health, and the National Center for Communicable Diseases, working in close collaboration with the WHO Country Office in Mongolia and the WHO Regional Office for the Western Pacific.
Mongolia is committed to ensuring that this evidence translates into concrete action, turning research into results and advancing the health and well-being of infants, mothers, and children, as part of the country’s broader milestones in vaccine preventable diseases prevention and control.