Leveraging a national biorepository in Zambia to assess measles and rubella immunity gaps across age and space

Abstract

High-quality, representative serological surveys allow direct estimates of immunity profiles to inform vaccination strategies but can be costly and logistically challenging. Leveraging residual serum samples is one way to increase their feasibility. We subsampled 9854 residual sera from a 2016 national HIV survey in Zambia and tested these specimens for anti-measles and anti-rubella virus IgG antibodies using indirect enzyme immunoassays. We demonstrate innovative methods for sampling residual sera and analyzing seroprevalence data, as well as the value of seroprevalence estimates to understand and control measles and rubella. National measles and rubella seroprevalence for individuals younger than 50 years was 82.8% (95% CI 81.6, 83.9%) and 74.9% (95% CI 73.7, 76.0%), respectively. Despite a successful childhood vaccination program, measles immunity gaps persisted across age groups and districts, indicating the need for additional activities to complement routine immunization. Prior to vaccine introduction, we estimated a rubella burden of 96 congenital rubella syndrome cases per 100,000 live births. Residual samples from large-scale surveys can reduce the cost and challenges of conducting serosurveys, and multiple pathogens can be tested. Procedures to access quality specimens, ensure ethical approvals, and link sociodemographic data can improve the timeliness and value of results.

Evaluating the effect of measles and rubella mass vaccination campaigns on seroprevalence in India: a before-and-after cross-sectional household serosurvey in four districts, 2018–2020

“…Although the purpose of the paired serosurveys in this study was to quantify the effect of the MR-SIA and identify remaining immunity gaps, serosurveys can also inform targeted SIAs or routine vaccination strategies. 20 , 21 Further analyses into epidemiological, financial, and logistical trade-offs of targeted versus nationwide, non-selective SIAs are needed.…”

Impact of disruptions to routine vaccination programs, quantifying burden of measles, and mapping targeted supplementary immunization activities

“…Coverage of first dose of measles-containing vaccine (MCV1) estimates (2018) acquired from the Zambia Health Management Information System (HMIS). Measles seropositivity estimates obtained from the biospecimens collected during 2016 Zambian Population HIV Impact Assessment ( Carcelen et al, 2022 ). Province MCV1 coverage, 2018 (%) Measles seropositivity, 2016 (%) Central 90 84.7 Copperbelt 85 82.7 Eastern 99 80.5 Luapula 99 78.2 Lusaka 91 82.9 Muchinga 96 86.1 Northern 94 87.0 North-Western 99 83.2 Southern 86 81.0 Western 98 83.4 …”

“…The susceptible population per time step was estimated by births, population sizes, and routine vaccination coverage for each district. The initial susceptible fractions were set to province-level seroprevalence estimates from biospecimens collected during 2016 Zambian Population HIV Impact Assessment ( Carcelen et al, 2022 ). Connectivity data were estimated using a gravity model fit to Namibia, a neighboring country in sub-Saharan Africa, and scaled with population sizes and distance reflective of districts within Zambia ( Carcelen et al, 2022 , Giles et al, 2021 ).…”

“…The initial susceptible fractions were set to province-level seroprevalence estimates from biospecimens collected during 2016 Zambian Population HIV Impact Assessment ( Carcelen et al, 2022 ). Connectivity data were estimated using a gravity model fit to Namibia, a neighboring country in sub-Saharan Africa, and scaled with population sizes and distance reflective of districts within Zambia ( Carcelen et al, 2022 , Giles et al, 2021 ). This model was used to simulate measles dynamics, interruptions to routine vaccination programs, and strategies for SIAs.…”

“…We investigated disruptions to routine vaccination services, subsequent outbreak risk, and SIA strategies in Zambia, a country of roughly 17.8 million persons in southern Africa (The World Bank, 2022) . Since 2010, there have been few reported cases of measles and overall high routine coverage of MCV1, with a national average of 90% ( Carcelen et al, 2022 , Katemba et al, 2019 ). However, despite high coverage, Zambia has been subject to measles outbreaks (Katemba et al, 2019) .…”