Who is missed in a community-based survey: Assessment and implications of biases due to incomplete sampling frame in a community-based serosurvey, Choma and Ndola Districts, Zambia, 2022.

Community-based serological studies are increasingly relied upon to measure disease burden, identify population immunity gaps, and guide control and elimination strategies; however, there is little understanding of the potential for and impact of sampling biases on outcomes of interest. As part of efforts to quantify measles immunity gaps in Zambia, a community-based serological survey using stratified multi-stage cluster sampling approach was conducted in Ndola and Choma districts in May-June 2022, enrolling 1245 individuals. We carried out a follow-up study among individuals missed from the sampling frame of the serosurvey in July-August 2022, enrolling 672 individuals. We assessed the potential for and impact of biases in the community-based serosurvey by i) estimating differences in characteristics of households and individuals included and excluded (77% vs 23% of households) from the sampling frame of the serosurvey and ii) evaluating the magnitude these differences make on healthcare-seeking behavior, vaccination coverage, and measles seroprevalence. We found that missed households were 20% smaller and 25% less likely to have children. Missed individuals resided in less wealthy households, had different distributions of sex and occupation, and were more likely to seek care at health facilities. Despite these differences, simulating a survey in which missed households were included in the sampling frame resulted in less than a 5% estimated bias in these outcomes. Although community-based studies are upheld as the gold standard study design in assessing immunity gaps and underlying community health characteristics, these findings underscore the fact that sampling biases can impact the results of even well-conducted community-based surveys. Results from these studies should be interpreted in the context of the study methodology and challenges faced during implementation, which include shortcomings in establishing accurate and up-to-date sampling frames. Failure to account for these shortcomings may result in biased estimates and detrimental effects on decision-making.

Measles immunity gaps among children and adolescents with HIV in Zambia despite high measles vaccination and antiretroviral therapy coverage.

OBJECTIVE: The study objective was to identify measles and rubella immunity gaps among people with HIV (PWH) in Zambia despite high measles vaccine coverage and widespread access to antiretroviral therapy. DESIGN: Nationally representative cross-sectional serosurvey using biorepository specimens. METHODS: Blood specimens collected in the Zambia Population HIV Impact Assessment survey (ZAMPHIA) of 2016 were tested for measles and rubella immunoglobulin G (IgG) antibodies by enzyme immunoassay. Hierarchical generalized additive models were fit to characterize age-specific measles and rubella seroprevalence profiles by HIV infection status. Log-binomial regression was performed to identify factors associated with seronegativity. RESULTS: Of the 25 383 specimens, a subsample of 11 500 were selected and 9852 (85%) were successfully tested. Measles seroprevalence was lower among PWH compared with HIV-uninfected individuals until approximately 30 years of age. Among children younger than the age of 10 years, measles seroprevalence was 47.2% [95% confidence interval (CI): 32.7, 61.7] in PWH and 76.4% (95% CI: 74.9, 78.0) in HIV-uninfected children in same age category. In contrast, rubella seroprevalence was higher among PWH than HIV-uninfected individuals, particularly for children younger than 10 years (68.6% vs. 44.3%, P  < 0.001). Having a detectable viral load was associated with being measles seronegative (adjusted prevalence ratio 0.15, 95% CI: 0.06, 0.38). CONCLUSIONS: These results from a nationally representative serosurvey demonstrate persistence of measles immunity gaps among PWH younger than 30 years of age. There is need to implement the World Health Organization's recommendation to revaccinate children living with HIV against measles following immune reconstitution with antiretroviral therapy to protect these children and prevent measles outbreaks.

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

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.

COVID-19 vaccine hesitancy in Zambia: a glimpse at the possible challenges ahead for COVID-19 vaccination rollout in sub-Saharan Africa.

With unprecedented speed, multiple vaccines against SARS-CoV-2 are available 1 year after the COVID-19 pandemic was first identified. As we push to achieve global control through these new vaccines, old challenges present themselves, including cold-chain storage, the logistics of mass vaccination, and vaccine hesitancy. Understanding how much hesitancy toward COVID-19 vaccines might occur and what factors may be driving these concerns can improve the ability of public health workers and communicators to maximize vaccine uptake. We nested a survey within a measles-rubella mass vaccination campaign in Zambia in November 2020 and asked about sentiments and beliefs toward COVID-19 and COVID-19 vaccines. Among parents bringing their children to receive a measles-rubella vaccine, we found high acceptability of COVID-19 vaccination of their children, but substantial uncertainty and hesitancy about receiving the vaccine themselves. COVID-19 vaccination hesitancy was correlated with beliefs around COVID-19 severity and risk, as well as vaccine safety and effectiveness.