Estimating the immunogenicity of measles-rubella vaccination administered during a mass campaign in Lao People’s Democratic Republic using multi-valent seroprevalence data

Abstract

Measles and rubella are important causes of morbidity and mortality globally. Despite high coverage reported for measles vaccination, outbreaks continue to occur in some countries. The reasons for these outbreaks are poorly understood. We apply Bayesian methods to multi-valent seroprevalence data for measles and rubella, collected 2 years and 3 months after a mass measles-rubella vaccination campaign in Lao PDR to estimate the immunogenicity and vaccination coverage. When the vaccination coverage was constrained to exceed 95% or 90%, consistent with officially-reported values, the immunogenicity of the measles vaccine component was unexpectedly low (75% (95% CR: 63–82%) and 79% (CR: 70–87%) respectively. The estimated immunogenicity increased after relaxing constraints on the vaccination coverage, with best-fitting values of 83% (95% CR: 73–91%) and 97% (95% CR: 90–100%) for the measles and rubella components respectively, with an estimated coverage of 83% (95% CR: 80–88%). The findings suggest that, if the vaccine coverage was as high as that reported, continuing measles outbreaks in Lao PDR, and potentially elsewhere, may be attributable to suboptimal immunogenicity attained in mass campaigns. Vaccine management in countries with high reported levels of coverage and ongoing measles outbreaks needs to be reviewed if measles elimination targets are to be achieved.

Susceptibility to Vaccine-Preventable Diseases in Four Districts of Xaysomboun Province, Lao People’s Democratic Republic

“…Seroprotection against rubella in our study was higher than measles in all age groups with 91.2% overall. This is similar to other provinces [ 27 ] and high seroprevalence in children could reflect wild-type rubella circulation [ 32 ], or vaccination—suggesting a difference in immunogenicity between measles and rubella components of the MR vaccine [ 14 , 33 ]. In contrast, the high seroprevalence in adults born before introduction of rubella vaccination in 2011 is likely to be due to rubella virus infection or SIA for younger adults.…”

Age-stratified seroprevalence of vaccine-preventable infectious disease in Saravan, Southern Lao People’s Democratic Republic

“…The significant increase of measles seroprevalence in the older age groups probably indicates cumulative wildtype exposure with age or possibly inclusion in SIA such as that in 2011 which covered children aged 9 months to 19 years (approximately 9-30 years at the time of the study) (Hachiya et al, 2018;World Health Organization, 2020). Several recent measles outbreaks in Lao PDR, including 1119reported cases in 2019(World Health Organization, 2020, have likely resulted from low vaccination coverage and compromised vaccine immunogenicity (Vynnycky et al, 2019) (Hefele et al, manuscript in preparation). Interestingly, seroprevalence was particularly high in the Inh ethnic group (93.1%) perhaps reflecting wild-type virus circulation.…”

Factors contributing to a measles outbreak in a hard-to-reach rural village in Xaisomboun Province, Lao People’s Democratic Republic

“…A reduction in immunogenicity related to suboptimal vaccine handling and poor immune response during the national measles campaign in 2011 have previously been proposed and may also be contributory. ( 12 )…”