Comparative Estimates of Crude and Effective Coverage of Measles Immunization in Low-Resource Settings: Findings from Salud Mesoamérica 2015

Abstract

Timely and accurate measurement of population protection against measles is critical for decision-making and prevention of outbreaks. However, little is known about how survey-based estimates of immunization (crude coverage) compare to the seroprevalence of antibodies (effective coverage), particularly in low-resource settings. In poor areas of Mexico and Nicaragua, we used household surveys to gather information on measles immunization from child health cards and caregiver recall. We also collected dried blood spots (DBS) from children aged 12 to 23 months to compare crude and effective coverage of measles immunization. We used survey-weighted logistic regression to identify individual, maternal, household, community, and health facility characteristics that predict gaps between crude coverage and effective coverage. We found that crude coverage was significantly higher than effective coverage (83% versus 68% in Mexico; 85% versus 50% in Nicaragua). A large proportion of children (19% in Mexico; 43% in Nicaragua) had health card documentation of measles immunization but lacked antibodies. These discrepancies varied from 0% to 100% across municipalities in each country. In multivariate analyses, card-positive children in Mexico were more likely to lack antibodies if they resided in urban areas or the jurisdiction of De Los Llanos. In contrast, card-positive children in Nicaragua were more likely to lack antibodies if they resided in rural areas or the North Atlantic region, had low weight-for-age, or attended health facilities with a greater number of refrigerators. Findings highlight that reliance on child health cards to measure population protection against measles is unwise. We call for the evaluation of immunization programs using serological methods, especially in poor areas where the cold chain is likely to be compromised. Identification of within-country variation in effective coverage of measles immunization will allow researchers and public health professionals to address challenges in current immunization programs.

Coverage and timeliness of vaccination and the validity of routine estimates: Insights from a Vaccine Registry in Kenya

“…In any setting with delays in vaccination, 'up-to-date coverage' will be a biased measure of vaccination-induced population immunity (38) and this bias, always over-estimating protection, can be as great as 24% in our survey. (38)(39)(40) AUC is a better measure because it provides an estimate of mean vaccination coverage throughout the period of risk. However, true population immunity will be lower than the AUC because a small proportion of vaccinated children will not develop an appropriate antibody response either because of operational factors (ineffective administration, inactive vaccine, heat destroyed vaccine, etc.)…”

Seroepidemiology: an underused tool for designing and monitoring vaccination programmes in low‐ and middle‐income countries

“…Oral fluid performed well in studies in Ethiopia and Kenya but poorly in Bangladesh . A study using DBS in poor areas of Mexico and Nicaragua found very low measles antibody prevalence (68% and 50%, respectively) despite high reported vaccination coverage and successful measles elimination in both countries . Although the study showed internal consistency in that antibody prevalence was lowest in areas with known cold chain or vaccination recording problems, it is hard to reconcile this low prevalence with the absence of measles outbreaks.…”

“…In settings where infections are eliminated or near elimination and there are very few disease notifications, serosurveillance can detect immunity gaps before outbreaks occur. Causes of immunity gaps include failure to vaccinate certain population groups , in‐migration of unvaccinated persons , reduced vaccine effectiveness or waning vaccine‐induced immunity . Ideally, immunity gaps are identified in time to prevent outbreaks.…”

“…Although of limited use to measure vaccine coverage, measles serosurveys can highlight potential problems with storing, administering or recording measles vaccination. A recent study in poor areas of Mexico and Nicaragua found that high proportions of children aged 12–23 months with documented measles vaccination were seronegative and that these children were clustered in certain municipalities, raising concerns about vaccination practices in those areas .…”

Serological Monitoring Is Key To Sustain Progress of the Maternal and Neonatal Tetanus Elimination Initiative

“…In addition, equipment is required, as described by Scobie et al (15) and others (27), to maintain a reverse cold/freeze chain. The use of dried blood spots (DBS) does not obviate a needle stick but does eliminate the requirement for a cold/freeze chain (28,29). However, once back in the reference laboratory the DBS must undergo a cumbersome elution step to obtain quasiserum for testing.…”