Absence of association between cord specific antibody levels and severe respiratory syncytial virus (RSV) disease in early infants: A case control study from coastal Kenya

PLoS ONE, Volume 11, No. 11, Year 2016

Interpretation

Background: The target group for severe respiratory syncytial virus (RSV) disease prevention is infants under 6 months of age. Vaccine boosting of antibody titres in pregnant mothers could protect these young infants from severe respiratory syncytial virus (RSV) associated disease. Quantifying protective levels of RSV-specific maternal antibody at birth would inform vaccine development. Methods: A case control study nested in a birth cohort (2002-07) was conducted in Kilifi, Kenya; where 30 hospitalised cases of RSV-associated severe disease were matched to 60 controls. Participants had a cord blood and 2 subsequent 3-monthly blood samples assayed for RSV-specific neutralising antibody by the plaque reduction neutralisation test (PRNT). Two sample paired t test and conditional logistic regression were used in analyses of log2PRNT titres. Results: The mean RSV log2PRNT titre at birth for cases and controls were not significantly different (P = 0.4) and remained so on age-stratification. Cord blood PRNT titres showed considerable overlap between cases and controls. The odds of RSV disease decreased with increase in log2PRNT cord blood titre. There was a 30% reduction in RSV disease per unit increase in log2PRNT titre (<3months age group) but not significant (P = 0.3). Conclusions: From this study, there is no strong evidence of protection by maternal RSV specific antibodies from severe RSV disease. Cord antibody levels show wide variation with considerable overlap between cases and controls. It is likely that, there are additional factors to specific PRNT antibody levels which determine susceptibility to severe RSV disease. In addition, higher levels of neutralizing antibody beyond the normal range may be required for protection; which it is hoped can be achieved by a maternal RSV vaccine. This study was conducted in Kilifi, the coastal part of Kenya [20]. The study was nested within a previous birth cohort study. Between 1999 and 2007, Kenya Medical Research Institute-Wellcome Trust Research Programme (KEMRI-WTRP), conducted a Kilifi Birth Cohort (KBC) study within the Kilifi Health and Demographic Surveillance System [20–22]. The KBC study was an observational study where participants were followed for a two-year period with a cord blood sample collected at birth and subsequent 3 monthly blood samples during follow ups. Details of the birth cohort study are described elsewhere [16, 21, 22]. The KBC study participants had access to Kilifi County Hospital (KCH) previously referred to as Kilifi District Hospital (KDH). We conducted a case-control study using archived serum or plasma samples from participants of the KBC study. We defined cases as infants who were admitted with severe pneumonia or lower respiratory tract infection (LRTI) within the first 6 months of life and had a positive RSV diagnosis by an Immunofluorescent Antibody Test (IFAT; Millipore, USA). Controls were infants who were not admitted to KCH with RSV associated severe pneumonia during the follow up period. Exposure to RSV infection among the controls was measured by screening cord blood and the 3 monthly subsequent samples for RSV IgA ELISA antibodies. An increase in RSV IgA antibodies detected either in the 3 or 6 month serum sample was used as a marker of exposure. Cases were matched to controls in a ratio of 1:2 by date of birth (within 30 days of date of birth) and geographical location. Every participant had a cord blood sample and two subsequent 3 months follow up blood samples. Continuous surveillance for RSV in paediatric admissions to KCH with syndromic severe or very severe pneumonia (using WHO criteria)[23] was in place throughout the KBC study with screening for RSV antigen by Immunofluorescent Antibody Test (IFAT)[24]. Enhanced detection of RSV cases missed by using the WHO pneumonia criteria was made by inclusion of children with a clinical admission diagnosis of LRTI. During the period for RSV surveillance, all paediatric admissions had blood samples collected for culture to diagnose invasive bacterial pathogens. A computerised system linking residents of the KHDSS and KCH admissions enabled identification of RSV positive hospital admission from the KBC. Furthermore, we investigated whether the level of neutralizing antibodies measured from RSV A2 infection differs according to the circulating strain within the population. To do this, an additional subset of 100 cord blood samples was randomly selected from the Kilifi birth Cohort study regardless of infection status and tested for neutralizing activity to a range of RSV virus strains. All parents and guardians gave written consent to have their children participate in the KBC study or paediatric RSV study at KCH and for storage of blood samples for use in future research. The use of the archived sample set was approved by the KEMRI-Ethical Review Committee. Cord blood and admission samples collected during the KBC study were immediately taken to the microbiology laboratory for processing and storage at -80°C. For this case control study, archived blood samples were retrieved and assayed for RSV neutralising antibody by a plaque reduction neutralisation assay. Serum samples were incubated at 56°C in a water bath for thirty minutes to inactivate complement cascade proteins; thereafter, plaque reduction neutralisation procedures were conducted as described elsewhere[25]. The dilution (and titre reciprocal) of a test serum sample required to induce 50% neutralization of a known titration of RSV A2 virus was determined using the Spearman Karber method. To account for any significant effect of freeze thaw on sample neutralization titres, a validation assay was carried out where a set of KBC samples previously screened (5 years interval); were retrieved, screened and the two PRNT titres results compared. A subset of 100 cord bloods collected over the same time period as for the case-control study were selected at random, stratified by year, from the KBC archive, as previously described [16]. These were screened for RSV specific neutralising antibodies by the method described above using 4 different strains i.e., RSV A2 (Australia, 1961), RSV B860 (Sweden, 1960), RSV A Kilifi (Kenya, 2005) and RSV B Kilifi (Kenya, 2005). Residues of samples from controls were tested for RSV-specific IgA antibodies by ELISA using crude virus extract from laboratory adapted RSV A2 culture[26] Specific antibody concentrations were recorded as log arbitrary units (AU) as determined by a local standards procedure[26]. The crude virus RSV lysate preparation was as previously described by Ochola et al[27]. All data analysis was conducted using STATA version 13.1 (College Station, Texas). Laboratory data for sample PRNT titres were logarithmically transformed (base 2) and merged with the KHDSS and clinical data for analyses. To quantify the level of RSV-specific maternal antibodies at birth that provide infant protection, mean PRNT titres were computed for cord blood samples. The difference in cord blood levels between the cases and controls were analysed using a two sample paired t test. For comparison, a two sample Wilcoxon rank-sum (Mann-Whitney) test was applied to the log2PRNT titres for cases and controls. Further comparison of the distribution of cord blood log-transformed PRNT titres between cases and controls was done using reverse cumulative distribution plots. The absolute reduction in risk of RSV disease per unit increase in cord blood antibody titres was calculated using modified conditional logistic regression methods[28]. The estimated rate of decay of RSV specific log2PRNT titres from birth to 6 months of life was determined by simple linear regression, accounting for clustering of titres for samples from the same individual using the procedure for Huber-White sandwich estimator. Elimination of bias on the rate of decay arising from RSV infection was done as previously described [16]i.e.: the titre of cord, first and second samples for an individual were defined as TC, T1 and T2, respectively. For individuals with T1≥TC, all results for that individual were excluded, and for individuals with T2≥T1 the result for sample T2 was excluded. In addition, results from samples collected from cases after an infection was identified were excluded. Comparison of the estimated rate of decay was conducted using a two sample paired t-test. To further control for the difference in the estimated rate of decay between cases and controls within a match set, a linear regression model with an interaction effect between age and case/control was used. The association between the concentration of maternal antibody titres and gestational age (measured by clinical evaluation or based on date of last menstruation) and birth weight (measured using a weighing scale at birth) was assessed. The odds of severe RSV disease in the first 6 months of life was determined, adjusting for the potential confounders of prematurity (i.e. gestational age < 37 weeks) and low birth weight (i.e. <2.5Kg) as categorical variables, using conditional logistic regression methods[28]. To ascertain exposure among controls, a defined cut off value was computed from the mean cord blood IgA log AU plus 3 standard deviations. Any of the 3 or 6 months serum samples with an IgA level above this cut off value were defined as exposed and those below this cut off as unexposed.

AI Digest

Study Justification:

– The study aimed to investigate the association between cord specific antibody levels and severe respiratory syncytial virus (RSV) disease in early infants.
– The target group for severe RSV disease prevention is infants under 6 months of age, and understanding the role of maternal antibodies in protecting these infants is important for vaccine development.

Study Highlights:

– The study was conducted in Kilifi, Kenya, as part of a larger birth cohort study.
– 30 hospitalised cases of RSV-associated severe disease were matched to 60 controls.
– Cord blood and subsequent blood samples were assayed for RSV-specific neutralising antibody.
– The mean RSV antibody levels at birth were not significantly different between cases and controls.
– The odds of RSV disease decreased with an increase in cord blood antibody levels, but this was not statistically significant.
– Cord blood antibody levels showed wide variation and considerable overlap between cases and controls.

Study Recommendations:

– The study suggests that there is no strong evidence of protection by maternal RSV-specific antibodies from severe RSV disease.
– Additional factors, beyond specific antibody levels, may determine susceptibility to severe RSV disease.
– Higher levels of neutralizing antibody may be required for protection, which could potentially be achieved through a maternal RSV vaccine.

Key Role Players:

– Researchers and scientists involved in RSV vaccine development and maternal health.
– Healthcare professionals and policymakers responsible for implementing RSV prevention strategies.
– Community health workers and educators who can disseminate information about RSV and vaccination.

Cost Items for Planning Recommendations:

– Research and development costs for a maternal RSV vaccine.
– Costs associated with vaccine production, distribution, and administration.
– Training and education costs for healthcare professionals and community health workers.
– Costs for public awareness campaigns and educational materials.
– Monitoring and evaluation costs to assess the effectiveness of RSV prevention strategies.

Strength of Evidence

The strength of evidence for this abstract is 7 out of 10.
The evidence in the abstract is moderately strong, but there are some areas for improvement. The study design is a case-control study nested within a birth cohort, which provides a good level of evidence. The statistical analyses used are appropriate, including t-tests and logistic regression. However, the sample size is relatively small, with only 30 cases and 60 controls, which may limit the generalizability of the findings. Additionally, the study could benefit from further exploration of potential confounders, such as maternal age and socioeconomic status. To improve the strength of the evidence, future studies could consider increasing the sample size and including a more diverse population. Additionally, conducting a prospective cohort study with a larger number of cases and controls would provide stronger evidence.

Abstract

This study was conducted in Kilifi, the coastal part of Kenya [20]. The study was nested within a previous birth cohort study. Between 1999 and 2007, Kenya Medical Research Institute-Wellcome Trust Research Programme (KEMRI-WTRP), conducted a Kilifi Birth Cohort (KBC) study within the Kilifi Health and Demographic Surveillance System [20–22]. The KBC study was an observational study where participants were followed for a two-year period with a cord blood sample collected at birth and subsequent 3 monthly blood samples during follow ups. Details of the birth cohort study are described elsewhere [16, 21, 22]. The KBC study participants had access to Kilifi County Hospital (KCH) previously referred to as Kilifi District Hospital (KDH). We conducted a case-control study using archived serum or plasma samples from participants of the KBC study. We defined cases as infants who were admitted with severe pneumonia or lower respiratory tract infection (LRTI) within the first 6 months of life and had a positive RSV diagnosis by an Immunofluorescent Antibody Test (IFAT; Millipore, USA). Controls were infants who were not admitted to KCH with RSV associated severe pneumonia during the follow up period. Exposure to RSV infection among the controls was measured by screening cord blood and the 3 monthly subsequent samples for RSV IgA ELISA antibodies. An increase in RSV IgA antibodies detected either in the 3 or 6 month serum sample was used as a marker of exposure. Cases were matched to controls in a ratio of 1:2 by date of birth (within 30 days of date of birth) and geographical location. Every participant had a cord blood sample and two subsequent 3 months follow up blood samples. Continuous surveillance for RSV in paediatric admissions to KCH with syndromic severe or very severe pneumonia (using WHO criteria)[23] was in place throughout the KBC study with screening for RSV antigen by Immunofluorescent Antibody Test (IFAT)[24]. Enhanced detection of RSV cases missed by using the WHO pneumonia criteria was made by inclusion of children with a clinical admission diagnosis of LRTI. During the period for RSV surveillance, all paediatric admissions had blood samples collected for culture to diagnose invasive bacterial pathogens. A computerised system linking residents of the KHDSS and KCH admissions enabled identification of RSV positive hospital admission from the KBC. Furthermore, we investigated whether the level of neutralizing antibodies measured from RSV A2 infection differs according to the circulating strain within the population. To do this, an additional subset of 100 cord blood samples was randomly selected from the Kilifi birth Cohort study regardless of infection status and tested for neutralizing activity to a range of RSV virus strains. All parents and guardians gave written consent to have their children participate in the KBC study or paediatric RSV study at KCH and for storage of blood samples for use in future research. The use of the archived sample set was approved by the KEMRI-Ethical Review Committee. Cord blood and admission samples collected during the KBC study were immediately taken to the microbiology laboratory for processing and storage at -80°C. For this case control study, archived blood samples were retrieved and assayed for RSV neutralising antibody by a plaque reduction neutralisation assay. Serum samples were incubated at 56°C in a water bath for thirty minutes to inactivate complement cascade proteins; thereafter, plaque reduction neutralisation procedures were conducted as described elsewhere[25]. The dilution (and titre reciprocal) of a test serum sample required to induce 50% neutralization of a known titration of RSV A2 virus was determined using the Spearman Karber method. To account for any significant effect of freeze thaw on sample neutralization titres, a validation assay was carried out where a set of KBC samples previously screened (5 years interval); were retrieved, screened and the two PRNT titres results compared. A subset of 100 cord bloods collected over the same time period as for the case-control study were selected at random, stratified by year, from the KBC archive, as previously described [16]. These were screened for RSV specific neutralising antibodies by the method described above using 4 different strains i.e., RSV A2 (Australia, 1961), RSV B860 (Sweden, 1960), RSV A Kilifi (Kenya, 2005) and RSV B Kilifi (Kenya, 2005). Residues of samples from controls were tested for RSV-specific IgA antibodies by ELISA using crude virus extract from laboratory adapted RSV A2 culture[26] Specific antibody concentrations were recorded as log arbitrary units (AU) as determined by a local standards procedure[26]. The crude virus RSV lysate preparation was as previously described by Ochola et al[27]. All data analysis was conducted using STATA version 13.1 (College Station, Texas). Laboratory data for sample PRNT titres were logarithmically transformed (base 2) and merged with the KHDSS and clinical data for analyses. To quantify the level of RSV-specific maternal antibodies at birth that provide infant protection, mean PRNT titres were computed for cord blood samples. The difference in cord blood levels between the cases and controls were analysed using a two sample paired t test. For comparison, a two sample Wilcoxon rank-sum (Mann-Whitney) test was applied to the log2PRNT titres for cases and controls. Further comparison of the distribution of cord blood log-transformed PRNT titres between cases and controls was done using reverse cumulative distribution plots. The absolute reduction in risk of RSV disease per unit increase in cord blood antibody titres was calculated using modified conditional logistic regression methods[28]. The estimated rate of decay of RSV specific log2PRNT titres from birth to 6 months of life was determined by simple linear regression, accounting for clustering of titres for samples from the same individual using the procedure for Huber-White sandwich estimator. Elimination of bias on the rate of decay arising from RSV infection was done as previously described [16]i.e.: the titre of cord, first and second samples for an individual were defined as TC, T1 and T2, respectively. For individuals with T1≥TC, all results for that individual were excluded, and for individuals with T2≥T1 the result for sample T2 was excluded. In addition, results from samples collected from cases after an infection was identified were excluded. Comparison of the estimated rate of decay was conducted using a two sample paired t-test. To further control for the difference in the estimated rate of decay between cases and controls within a match set, a linear regression model with an interaction effect between age and case/control was used. The association between the concentration of maternal antibody titres and gestational age (measured by clinical evaluation or based on date of last menstruation) and birth weight (measured using a weighing scale at birth) was assessed. The odds of severe RSV disease in the first 6 months of life was determined, adjusting for the potential confounders of prematurity (i.e. gestational age < 37 weeks) and low birth weight (i.e. <2.5Kg) as categorical variables, using conditional logistic regression methods[28]. To ascertain exposure among controls, a defined cut off value was computed from the mean cord blood IgA log AU plus 3 standard deviations. Any of the 3 or 6 months serum samples with an IgA level above this cut off value were defined as exposed and those below this cut off as unexposed.

Materials

Innovations

Based on the information provided, it appears that the study is focused on investigating the association between cord specific antibody levels and severe respiratory syncytial virus (RSV) disease in early infants. The study aims to determine if boosting antibody levels in pregnant mothers could protect young infants from severe RSV-associated disease. The study was conducted in Kilifi, Kenya, and involved a case-control design using archived serum or plasma samples from participants of a previous birth cohort study.

In terms of potential innovations to improve access to maternal health, here are a few recommendations:

1. Maternal RSV vaccine development: The study suggests that higher levels of neutralizing antibodies may be required for protection against severe RSV disease. This finding could inform the development of a maternal RSV vaccine that can boost antibody levels in pregnant mothers, potentially providing better protection for infants.

2. Improved screening and diagnosis: The study used the Immunofluorescent Antibody Test (IFAT) to diagnose RSV infection. Innovations in diagnostic technologies, such as rapid point-of-care tests or molecular assays, could improve the accuracy and speed of RSV diagnosis, leading to earlier interventions and better management of RSV-associated diseases.

3. Enhanced surveillance systems: The study relied on continuous surveillance for RSV in pediatric admissions to a hospital. Implementing robust and comprehensive surveillance systems for maternal health, including RSV and other relevant infections, could help identify high-risk populations and guide targeted interventions.

4. Integrated care models: To improve access to maternal health services, implementing integrated care models that combine antenatal care, immunization services, and postnatal care could ensure comprehensive and continuous care for pregnant women and their infants. This approach could facilitate the delivery of maternal vaccines, including RSV vaccines, and improve overall maternal and child health outcomes.

5. Community engagement and education: Increasing awareness and understanding of maternal health, including the importance of vaccination and preventive measures, among communities and healthcare providers can help improve access to maternal health services. Innovative approaches, such as community-based education programs and mobile health technologies, could be utilized to reach remote or underserved populations.

These recommendations are based on the information provided and aim to address the specific context of improving access to maternal health in relation to the study on RSV disease.

AI Innovations Description

Based on the description provided, the recommendation to improve access to maternal health would be to develop a maternal respiratory syncytial virus (RSV) vaccine. The study found that there is no strong evidence of protection by maternal RSV-specific antibodies from severe RSV disease in infants. However, it suggests that boosting antibody levels in pregnant mothers through vaccination could potentially protect young infants from severe RSV-associated disease. Therefore, developing a maternal RSV vaccine could be an innovative solution to improve access to maternal health and reduce the risk of severe RSV disease in infants.

AI Innovations Methodology

Based on the provided information, here are some potential recommendations to improve access to maternal health:

1. Implement mobile health (mHealth) solutions: Develop mobile applications or text messaging services that provide pregnant women with information on prenatal care, nutrition, and warning signs during pregnancy. These mHealth solutions can also be used to schedule appointments, remind women of upcoming check-ups, and provide access to telemedicine consultations.

2. Strengthen community-based healthcare: Establish and support community health workers who can provide maternal health services, including prenatal care, education, and referrals. These workers can reach remote areas and provide personalized care to pregnant women, improving access to essential services.

3. Improve transportation infrastructure: Enhance transportation networks in rural and underserved areas to ensure that pregnant women can easily access healthcare facilities. This can involve building roads, providing transportation subsidies, or implementing telemedicine services for remote consultations.

4. Increase availability of skilled birth attendants: Train and deploy more skilled birth attendants, such as midwives and nurses, in areas with limited access to healthcare facilities. These attendants can provide safe and quality care during childbirth, reducing maternal and neonatal mortality rates.

5. Strengthen health systems: Invest in improving healthcare infrastructure, equipment, and supplies in maternal health facilities. This includes ensuring the availability of essential medicines, equipment for safe deliveries, and emergency obstetric care.

To simulate the impact of these recommendations on improving access to maternal health, a methodology could include the following steps:

1. Define indicators: Identify key indicators to measure the impact of the recommendations, such as the number of prenatal care visits, the percentage of births attended by skilled birth attendants, or the reduction in maternal mortality rates.

2. Collect baseline data: Gather data on the current state of maternal health access in the target area, including the number of healthcare facilities, the availability of skilled birth attendants, and the utilization of prenatal care services.

3. Simulate interventions: Use modeling techniques to simulate the implementation of the recommendations. This can involve estimating the number of additional healthcare workers needed, the cost of infrastructure improvements, or the expected increase in prenatal care visits.

4. Analyze impact: Assess the projected impact of the interventions on the defined indicators. This can be done by comparing the simulated scenario with the baseline data, estimating the potential improvements in access to maternal health services.

5. Refine and adjust: Iterate the simulation model based on feedback and refine the interventions to optimize their impact. This may involve adjusting the scale or timing of the interventions or considering additional factors that may influence access to maternal health.

6. Monitor and evaluate: Implement a monitoring and evaluation plan to track the progress of the interventions and measure their actual impact on improving access to maternal health. This can involve regular data collection, analysis, and reporting to inform decision-making and further refine the interventions if needed.

Author

Dima Health

Statistics:

Citations: 20

Identifiers:

DOI: 10.1371/journal.pone.0166706

Research Areas:

Community Interventions, Environmental, Health System and Policy, Maternal and Child Health, Quality of Care, Sexual and Reproductive Health

Study Countries:

Kenya

Study Design:

Case-Control Study, Cohort Study, Cross Sectional Study

Study Approach:

Quantitative