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. 2024 Jun 20;12(6):695.
doi: 10.3390/vaccines12060695.

Breakthrough Measles among Vaccinated Adults Born during the Post-Soviet Transition Period in Mongolia

José E Hagan  1 , Stephen N Crooke  2 , Nyamaa Gunregjav  3 , Sun B Sowers  2 , Sara Mercader  2 , Carole J Hickman  2 , Mick N Mulders  4 , Roberta Pastore  1 , Yoshihiro Takashima  1 , David N Durrheim  5 , James L Goodson  6 , Paul A Rota  2
Affiliations

Breakthrough Measles among Vaccinated Adults Born during the Post-Soviet Transition Period in Mongolia

José E Hagan et al. Vaccines (Basel). .

Abstract

Mongolia experienced a nationwide measles outbreak during 1 March 2015-31 December 2016, with 49,077 cases reported to the WHO; many were among vaccinated young adults, suggesting a possible role of vaccine failure. Advanced laboratory methods, coupled with detailed epidemiological investigations, can help classify cases as vaccine failure, failure to vaccinate, or both. In this report, we conducted a study of cases to identify risk factors for breakthrough infection for a subset of laboratory-confirmed measles cases. Of the 193 cases analyzed, only 19 (9.8%) reported measles vaccination history, and 170 (88%) were uncertain. Measles-specific IgG avidity testing classified 120 (62%) cases as low IgG avidity, indicating no prior exposure to measles. Ten of these cases with low IgG avidity had a history of measles vaccination, indicating primary vaccine failure. Overall, sixty cases (31%) had high IgG avidity, indicating breakthrough infection after prior exposure to measles antigen through vaccination or natural infection, but the IgG avidity results were highly age-dependent. This study found that among young children aged 9 months-5 years, breakthrough infection was rare (4/82, 5%); however, among young adults aged 15-25 years, breakthrough infection due to secondary vaccine failure (SVF) occurred on a large scale during this outbreak, accounting for the majority of cases (42/69 cases, 61%). The study found that large-scale secondary vaccine failure occurred in Mongolia, which highlights the potential for sustained outbreaks in post-elimination settings due to "hidden" cohorts of young adults who may have experienced waning immunity. This phenomenon may have implications for the sustainability of measles elimination in countries that remain vulnerable to the importation of the virus from areas where it is still endemic. Until global measles elimination is achieved, enhanced surveillance and preparedness for future outbreaks in post- or peri-elimination countries may be required.

Keywords: IgG Avidity; Mongolia; breakthrough infection; measles elimination; measles outbreak; vaccine failure.

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Conflict of interest statement

The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the U.S. Centers for Disease Control and Prevention. The authors affiliated with the World Health Organization (WHO) are alone responsible for the views expressed in this publication and they do not necessarily represent the decisions or policies of the WHO. The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Comparison of age distribution of outbreak cases (source: case-based surveillance data officially submitted to WHO) and study cases.
Scheme 1
Scheme 1
Measles cases, by breakthrough infection classification and by birth year, Mongolia, 1 March 2015–17 April 2016, N = 193.
Scheme 2
Scheme 2
Age-specific attack rate during the 2015 outbreak in Mongolia (left y axis) and historical overview of routine and supplemental measles-containing vaccination coverage (right y axis)—Mongolia, 1987–2015. Reproduced with permission from Ref. [4], 2017, Oxford University Press.
Figure 2
Figure 2
Box–violin plot of measles case ages, by IgG avidity classification, Mongolia, 1 March 2015–17 April 2016, N = 193.
See this image and copyright information in PMC

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