Immunity levels to poliovirus in Lao children and adults before the vaccine-derived poliovirus outbreak: A retrospective study

Abstract

In 2015, several provinces in Lao People's Democratic Republic (Lao PDR) experienced a vaccine-derived poliovirus outbreak. This survey was conducted (i) to evaluate the vaccination coverage in different settings and cohorts using the seroprevalence of anti-poliovirus (PV) antibodies as a surrogate measure, and (ii) to explore the usefulness of an ELISA in a country with limited resources and a specific epidemiological setting. IgG antibodies were assessed by ELISA in Lao children (n = 1216) and adults (n = 1228), including blood donors and health care workers. Protective antibody titers against the 3 vaccine serotypes were determined by microneutralization (VNT) in a subset of participants. More than 92% of the children had anti-poliovirus antibodies, regardless of nutritional status or access to health care, highlighting the success of the vaccination outreach activities in the country. In contrast, anti-poliovirus seroprevalence reached only 81.7% in blood donors and 71.9% in health care workers. Participants born before the introduction of poliovirus vaccination in Lao PDR were considerably less likely to be seropositive. These findings align with the epidemiology of the outbreak. Neutralizing antibodies against at least one of the 3 poliovirus serotypes were detected in all children (99/99) and 93/99 had antibodies against all serotypes. Similarly, all health care workers had neutralizing antibodies against at least one and 92/99 against all serotypes. The comparison of both assays shows an acceptable underestimation of vaccine coverage in children by ELISA, but a low sensitivity of the ELISA in the adults. We show that the ELISA is a reasonable alternative to the VNT in particular in vaccinated children, that an improved version should be serotype specific, and that negativity thresholds should be revisited for optimal sensitivity and specificity. Thus, polio-free countries with an uncertain vaccination coverage and limited laboratory capacity, that are at risk of vaccine-derived poliovirus outbreaks or of re-importation of wild poliovirus may benefit from an improved ELISA for cohort studies to evaluate their immunization program in children.

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

“…against polio, measles and rubella. Despite the comprehensive vaccination programme, outbreaks of vaccine-preventable diseases (VPD) continue to occur, such as polio (Pauly et al, 2018), measles (Sengkeopraseuth et al, 2018), diphtheria (Nanthavong et al, 2015) and pertussis (Kleine et al, 2020). Outbreaks near to the borders with neighboring countries such as Vietnam have also raised fear of cross-border spread of disease.…”

Prediction of the Vaccine-derived Poliovirus Outbreak Incidence: A Hybrid Machine Learning Approach

“…Nonetheless, the improved ELISA must be serotype distinct, and negativity thresholds should be studied for the specificity and sensitivity. It should be noted that out of the five examined cohorts, both healthcare workers (cohort 5) and children (cohort 1) were analyzed by VNT 35 . The WOA-RVFL method handled the healthcare workers as a practical example of an adult with a high risk during the outbreak since they are at a higher risk for exposure to infections with a possibility to transfer the infection from a specific cohort to another.…”

“…Therefore, it is important to track the immunization and vaccination in professionals and to ensure their ability to perform critical caring for patients. The WOA-RVFL algorithm can observe the ELISA serologies of the other children and adult cohorts matched with results of groups that tested by VNT 35 . The WOA-RVFL suggests a high efficiency of outreach vaccination activities since the children from the remote area were equally well protected as the fully vaccinated children.…”

Factors associated with hepatitis B vaccination in Laos: findings from the multiple indicator cluster surveys in 2011/12 and 2017

“…In recent years, outbreaks of vaccine-preventable diseases have been reported. 2 , 3 , 4 , 5 Hepatitis B is endemic in Laos and the prevalence of the hepatitis B surface antigen (HBsAg; used as a marker for chronic infection) in the general population is estimated to be 5–6%, based on a recent study published in 2022. 6 Although several studies reported on HBsAg prevalence rates in blood donors, women and children in the past years, it is difficult to understand hepatitis B epidemiology in Laos due to large differences in study populations, study designs and study sites.…”