Pneumococcal carriage in children in Ulaanbaatar, Mongolia before and one year after the introduction of the 13-valent pneumococcal conjugate vaccine

Decline in pneumococcal vaccine serotype carriage, multiple-serotype carriage, and carriage density in Nepalese children after PCV10 introduction: A pre-post comparison study

BACKGROUND

Carriage studies are an efficient means for assessing pneumococcal conjugate vaccine effect in settings where pneumococcal disease surveillance programmes are not well established. In this study the effect of 10-valent pneumococcal conjugate vaccine (PCV10) introduction on pneumococcal carriage and density among Nepalese children using a bacterial microarray and qPCR was examined.

METHODS

PCV10 was introduced into the Nepalese infant immunisation schedule in August 2015. Nasopharyngeal swabs were collected from healthy Nepalese children in Kathmandu between April 2014 and December 2021. Samples were plated on blood agar, incubated overnight, and DNA extracted from plate sweeps. Pneumococcal serotyping was done using the Senti-SPv1.5 microarray (BUGS Bioscience, UK). DNA was extracted from swab media and qPCR performed for pneumococcal autolysin (lytA).

RESULTS

A significant decline in prevalence of PCV10 serotypes was observed when comparing pre-PCV10 with post-PCV10 collection periods (36.5 %, 454/1244 vs 10.3 %, 243/2353, p < 0.0001). Multiple-serotype carriage was also observed to significantly decline when comparing pre-PCV10 with post-PCV10 periods (31.4 %, 390/1244 vs 22.2 %, 522/2353, p < 0.0001). Additionally, a significant decline in median pneumococcal density was observed when comparing pre-PCV10 with post-PCV10 periods (3.3 vs 3.25 log10 GE/ml, p = 0.0196).

CONCLUSIONS

PCV10 introduction was associated with reduced, prevalence of all PCV10 serotypes, multiple serotype carriage, and pneumococcal carriage density.

Respiratory Syncytial Virus and Influenza Infections in Children in Ulaanbaatar, Mongolia, 2015-2021

BACKGROUND

Data available for RSV and influenza infections among children < 2 years in Mongolia are limited. We present data from four districts of Ulaanbaatar from April 2015 to June 2021.

METHODS

This study was nested in an enhanced surveillance project evaluating pneumococcal conjugate vaccine (PCV13) impact on the incidence of hospitalized lower respiratory tract infections (LRTIs). Our study was restricted to children aged < 2 years with arterial O2 saturation < 93% and children with radiological pneumonia. Nasopharyngeal (NP) swabs collected at admission were tested for RSV and influenza using qRT-PCR. NP swabs of all patients with radiological pneumonia and of a subset of randomly selected NP swabs were tested for S. pneumoniae (S.p.) by qPCR and for serotypes by culture and DNA microarray.

RESULTS

Among 5705 patients, 2113 (37.0%) and 386 (6.8%) had RSV and influenza infections, respectively. Children aged 2-6 months had a higher percentage of very severe RSV infection compared to those older than 6 months (42.2% versus 31.4%, p-value Fisher's exact = 0.001). S.p. carriage was detected in 1073/2281 (47.0%) patients. Among S.p. carriage cases, 363/1073 (33.8%) had S.p. and RSV codetection, and 82/1073 (7.6%) had S.p. and influenza codetection. S.p. codetection with RSV/influenza was not associated with more severe LRTIs, compared to only RSV/influenza cases.

CONCLUSION

In Mongolia, RSV is an important pathogen causing more severe LRTI in children under 6 months of age. Codetection of RSV or influenza virus and S.p. was not associated with increased severity.

Impact of childhood 13-valent pneumococcal conjugate vaccine introduction on adult pneumonia hospitalisations in Mongolia: a time series analysis

Background

Few studies have assessed the potential indirect effects of childhood pneumococcal conjugate vaccine (PCV) programs on the adult pneumonia burden in resource-limited settings. We evaluated the impact of childhood PCV13 immunisation on adult all-cause pneumonia following a phased program introduction from 2016.

Methods

We conducted a time-series analysis to assess changes in pneumonia hospitalisation incidence at four district hospitals in Mongolia. Adults (≥18 years) that met the clinical case definition for all-cause pneumonia were enrolled. A negative binomial mixed-effects model was used to assess the impact of PCV13 introduction on monthly counts of pneumonia admissions from January 2015-February 2022. We also performed a restricted analysis excluding the COVID-19 pandemic period. All models were stratified by age and assessed separately. Additional analyses assessed the robustness of our findings.

Findings

The average annual incidence of all-cause pneumonia hospitalisation was highest in adults 65+ years (62.81 per 10,000 population) and declined with decreasing age. After adjusting for the COVID-19 pandemic period, we found that rates of pneumonia hospitalisation remained largely unchanged over time. We did not observe a reduction in pneumonia hospitalisation in any age group. Results from restricted and sensitivity analyses were comparable to the primary results, finding limited evidence of a reduced pneumonia burden.

Interpretation

We did not find evidence of indirect protection against all-cause pneumonia in adults following childhood PCV13 introduction. Direct pneumococcal vaccination and other interventions should be considered to reduce burden of pneumonia among older adults.

Funding

Pfizer clinical research collaboration agreement (contract number: WI236621).

Effect of Pneumococcal Conjugate Vaccine on Pneumonia Incidence Rates among Children 2-59 Months of Age, Mongolia, 2015-2021

Starting in June 2016, the 13-valent pneumococcal conjugate vaccine (PCV13) was introduced into the routine immunization program of Mongolia by using a 2+1 dosing schedule, phased by district. We used prospective hospital surveillance to evaluate the vaccine's effect on pneumonia incidence rates among children 2-59 months of age over a 6-year period. Of 17,607 children with pneumonia, overall adjusted incidence rate ratios showed decreased primary endpoint pneumonia, very severe pneumonia, and probable pneumococcal pneumonia until June 2021. Results excluding and including the COVID-19 pandemic period were similar. Pneumonia declined in 3 districts that introduced PCV13 with catch-up campaigns but not in the 1 district that did not. After PCV13 introduction, vaccine-type pneumococcal carriage prevalence decreased by 44% and nonvaccine-type carriage increased by 49%. After PCV13 introduction in Mongolia, the incidence of more specific pneumonia endpoints declined in children 2-59 months of age; additional benefits were conferred by catch-up campaigns.

Nasopharyngeal carriage of Streptococcus pneumoniae among children <5 years of age in Indonesia prior to pneumococcal conjugate vaccine introduction

Pneumococcal conjugate vaccines (PCVs) prevent nasopharyngeal colonization with vaccine serotypes of Streptococcus pneumoniae, leading to reduced transmission of pneumococci and stronger population-level impact of PCVs. In 2017 we conducted a cross-sectional pneumococcal carriage study in Indonesia among children aged <5 years before 13-valent PCV (PCV13) introduction. Nasopharyngeal swabs were collected during visits to community integrated health service posts at one peri-urban and one rural study site. Specimens were analyzed by culture, and isolates were serotyped using sequential multiplex polymerase chain and Quellung reaction. Antibiotic susceptibility was performed by broth microdilution method. We enrolled 1,007 children in Gunungkidul District, Yogyakarta (peri-urban) and 815 in Southwest Sumba, East Nusa Tenggara (rural). Pneumococcal carriage prevalence was 30.9% in Gunungkidul and 87.6% in Southwest Sumba (combined: 56.3%). PCV13 serotypes (VT) carriage was 15.0% in Gunungkidul and 52.6% in Southwest Sumba (combined: 31.8%). Among pneumococcal isolates identified, the most common VT were 6B (16.4%), 19F (15.8%), and 3 (4.6%) in Gunungkidul (N = 323) and 6B (17.6%), 19F (11.0%), and 23F (9.3%) in Southwest Sumba (N = 784). Factors associated with pneumococcal carriage were age (1-2 years adjusted odds ratio (aOR) 1.9, 95% CI 1.4-2.5; 3-4 years aOR 1.5, 95% CI 1.1-2.1; reference <1 year), other children <5 years old in the household (aOR 1.5, 95% CI 1.1-2.0), and presence of ≥1 respiratory illness symptom (aOR 1.8, 95% CI 1.4-2.2). Overall, 61.5% of the pneumococcal isolates were non-susceptible to ≥1 antibiotic class and 13.2% were multi-drug non-susceptible (MDNS) (non-susceptible to ≥3 classes of antibiotics). Among 602 VT isolates, 73.9% were non-susceptible and 19.9% were MDNS. These findings are critical to establish a pre-PCV13 carriage prevalence and demonstrate the complexity in evaluating the impact of PCV13 introduction in Indonesia given the wide variability in the carriage prevalence as shown by the two study sites.

Streptococcus pneumoniae serotype 33G: genetic, serological, and structural analysis of a new capsule type

IMPORTANCE

Streptococcus pneumoniae (the pneumococcus) is a bacterial pathogen with the greatest burden of disease in Asia and Africa. The pneumococcal capsular polysaccharide has biological relevance as a major virulence factor as well as public health importance as it is the target for currently licensed vaccines. These vaccines have limited valency, covering up to 23 of the >100 known capsular types (serotypes) with higher valency vaccines in development. Here, we have characterized a new pneumococcal serotype, which we have named 33G. We detected serotype 33G in nasopharyngeal swabs (n = 20) from children and adults hospitalized with pneumonia, as well as healthy children in Mongolia. We show that the genetic, serological, and biochemical properties of 33G differ from existing serotypes, satisfying the criteria to be designated as a new serotype. Future studies should focus on the geographical distribution of 33G and any changes in prevalence following vaccine introduction.

A systematic review of pneumococcal conjugate vaccine impact on pneumococcal nasopharyngeal colonisation density in children under 5 years of age

BACKGROUND

High pneumococcal carriage density has been associated with severe pneumonia in some settings. The impact of pneumococcal conjugate vaccines (PCVs) on pneumococcal carriage density has been variable. The aim of this systematic literature review is to describe the effect of PCV7, PCV10 and PCV13 on pneumococcal colonisation density in children under five years old.

METHODS

We included peer reviewed English literature published between 2000 and 2021 to identify relevant articles using Embase, Medline and PubMed. Original research articles of any study design in countries where PCV has been introduced/studied were included. Quality (risk) assessment was performed using tools developed by the National Heart Brain and Lung Institute for inclusion in this review. We used a narrative synthesis to present results.

RESULTS

Ten studies were included from 1941 articles reviewed. There were two randomised controlled trials, two cluster randomised trials, one case control study, one retrospective cohort study and four cross sectional studies. Three studies used semiquantitative culture methods to determine density while the remaining studies used quantitative molecular techniques. Three studies reported an increase in density and three studies found a decrease in density among vaccinated compared with unvaccinated children. Four studies found no effect. There was considerable heterogeneity in the study populations, study design and laboratory methods.

CONCLUSION

There was no consensus regarding the impact of PCV on pneumococcal nasopharyngeal density. We recommend the use of standardised methods to evaluate PCV impact on density.

Factors associated with pneumococcal nasopharyngeal carriage: A systematic review

Pneumococcal disease is a major contributor to global childhood morbidity and mortality and is more common in low- and middle-income countries (LMICs) than in high-income countries. Pneumococcal carriage is a prerequisite for pneumococcal disease. Pneumococcal conjugate vaccine reduces vaccine-type carriage and disease. However, pneumococcal carriage and disease persist, and it is important to identify other potentially modifiable factors associated with pneumococcal carriage and determine if risk factors differ between low, middle, and high-income countries. This information may help inform pneumococcal disease prevention programs. This systematic literature review describes factors associated with pneumococcal carriage stratified by country income status and summarises pneumococcal carriage rates for included studies. We undertook a systematic search of English-language pneumococcal nasopharyngeal carriage studies up to 30th June 2021. Peer-reviewed studies reporting factors associated with overall pneumococcal nasopharyngeal carriage in healthy, community-based study populations were eligible for inclusion. Two researchers independently reviewed studies to determine eligibility. Results are presented as narrative summaries. This review is registered with PROSPERO, CRD42020186914. Eighty-two studies were included, and 46 (56%) were conducted in LMICs. There was heterogeneity in the factors assessed in each study. Factors positively associated with pneumococcal carriage in all income classification were young age, ethnicity, symptoms of respiratory tract infection, childcare attendance, living with young children, poverty, exposure to smoke, season, and co-colonisation with other pathogens. Breastfeeding and antibiotic use were protective against carriage in all income classifications. Median (interquartile range) pneumococcal carriage rates differed by income classification, ranging from 51% (19.3-70.2%), 38.5% (19.3-51.6%), 31.5% (19.0-51.0%), 28.5% (16.8-35.4%), (P = 0.005) in low-, lower-middle, upper-middle, and high-income classifications, respectively. Our findings suggest that where measured, factors associated with pneumococcal nasopharyngeal carriage are similar across income classifications, despite the highest pneumococcal carriage rates being in low-income classifications. Reducing viral transmission through vaccination and public health interventions to address social determinants of health would play an important role.

Nasopharyngeal pneumococcal carriage in South Asian infants: Results of observational cohort studies in vaccinated and unvaccinated populations

Background

Nasopharyngeal pneumococcal carriage (NPC) is a prerequisite for invasive pneumococcal disease and reduced carriage of vaccine serotypes is a marker for the protection offered by the pneumococcal conjugate vaccine (PCV). The present study reports NPC during the first year of life in a vaccinated (with PCV10) cohort in Bangladesh and an unvaccinated cohort in India.

Methods

A total of 450 and 459 infants were recruited from India and Bangladesh respectively within 0-7 days after birth. Nasopharyngeal swabs were collected at baseline, 18 and 36 weeks after birth. The swabs were processed for pneumococcal culture and identification of serotypes by the Quellung test and polymerase chain reaction (PCR). An identical protocol was applied at both sites.

Results

Prevalence of NPC was 48% in the Indian and 54.8% in the Bangladeshi cohort at 18 weeks. It increased to 53% and 64.8% respectively at 36 weeks. The average prevalence of vaccine serotypes was higher in the Indian cohort (17.8% vs 9.8% for PCV-10 and 26.1% vs17.6% for PCV-13) with 6A, 6B, 19F, 23F, and 19A as the common serotypes. On the other hand, the prevalence of non-vaccine serotypes was higher (43.6% vs 27.1% for non-PCV13) in the Bangladeshi cohort with 34, 15B, 17F, and 35B as the common serotypes. Overcrowding was associated with increased risk of pneumococcal carriage. The present PCV-13 vaccine would cover 28%-30% and 47%-48% serotypes in the Bangladeshi and Indian cohorts respectively.

Conclusions

South Asian infants get colonised with pneumococci early in infancy; predominantly vaccine serotypes in PCV naïve population (India) and non-vaccine serotypes in the vaccinated population (Bangladesh). These local findings are important to inform the public health policy and the development of higher valent pneumococcal vaccines.

Evaluation of the impact of childhood 13-valent pneumococcal conjugate vaccine introduction on adult pneumonia in Ulaanbaatar, Mongolia: study protocol for an observational study

BACKGROUND

Community-acquired pneumonia is an important cause of morbidity and mortality in adults. Approximately one-third of pneumonia cases can be attributed to the pneumococcus. Pneumococcal conjugate vaccines (PCVs) protect against colonisation with vaccine-type serotypes. The resulting decrease in transmission of vaccine serotypes leads to large indirect effects. There are limited data from developing countries demonstrating the impact of childhood PCV immunisation on adult pneumonia. There are also insufficient data available on the burden and severity of all-cause pneumonia and respiratory syncytial virus (RSV) in adults from low resource countries. There is currently no recommendation for adult pneumococcal vaccination with either pneumococcal polysaccharide vaccine or PCVs in Mongolia. We describe the protocol developed to evaluate the association between childhood 13-valent PCV (PCV13) vaccination and trends in adult pneumonia.

METHODS

PCV13 was introduced into the routine childhood immunisation schedule in Mongolia in a phased manner from 2016. In March 2019 we initiated active hospital-based surveillance for adult pneumonia, with the primary objective of evaluating trends in severe hospitalised clinical pneumonia incidence in adults 18 years and older in four districts of Ulaanbaatar. Secondary objectives include measuring the association between PCV13 introduction and trends in all clinically-defined pneumonia, radiologically-confirmed pneumonia, nasopharyngeal carriage of S. pneumoniae and pneumonia associated with RSV or influenza. Clinical questionnaires, nasopharyngeal swabs, urine samples and chest radiographs were collected from enrolled patients. Retrospective administrative and clinical data were collected for all respiratory disease-related admissions from January 2015 to February 2019.

DISCUSSION

Establishing a robust adult surveillance system may be an important component of monitoring the indirect impact of PCVs within a country. Monitoring indirect impact of childhood PCV13 vaccination on adult pneumonia provides additional data on the full public health impact of the vaccine, which has implications for vaccine efficiency and cost-effectiveness. Adult surveillance in Mongolia will contribute to the limited evidence available on the burden of pneumococcal pneumonia among adults in low- and middle-income countries, particularly in the Asia-Pacific region. In addition, it is one of the few examples of implementing prospective, population-based pneumonia surveillance to evaluate the indirect impact of PCVs in a resource-limited setting.

Direct and indirect effects of 13-valent pneumococcal conjugate vaccine on pneumococcal carriage in children hospitalised with pneumonia from formal and informal settlements in Mongolia: an observational study

Background

Within Ulaanbaatar, Mongolia, risk factors for pneumonia are concentrated among children living in informal settlements comprised of temporary shelters (gers). We used pneumococcal carriage surveillance among children from formal and informal settlements hospitalised with pneumonia to evaluate the direct and indirect effects of 13-valent pneumococcal conjugate vaccine (PCV13) against vaccine-type (VT) pneumococcal carriage following a phased introduction of PCV13.

Methods

We enrolled and collected nasopharyngeal swabs from children 2-59 months of age presenting to hospital. Pneumococci were detected using lytA qPCR and serotyped using microarray on a random monthly selection of swabs between November 2015 and March 2019 from two districts in Ulaanbaatar. PCV13 status was determined using written records. We quantified the associations between individual PCV13 status (direct effects) and district-level PCV13 coverage (indirect effects) and VT carriage using generalised estimating equations and explored interactions by settlement type.

Findings

A total of 1 292 swabs from 6 046 participants were tested for pneumococci. Receipt of PCV13 and increasing PCV13 coverage independently reduced the risk of VT carriage. For each percent increase in PCV13 coverage, the adjusted odds of VT carriage decreased by 1•0% (OR 95% CI 0•983-0•996; p=0•001), with a predicted decrease in VT carriage rate from 29•1% to 13•1% as coverage reached 100%. There was a trend towards a slower decline within informal settlements (p=0•100). Adjusted PCV13 vaccine effectiveness against VT carriage was 39•1% (95% CI 11•4-58•1%, p=0•009).

Interpretation

Substantial indirect effects were observed following PCV13 introduction, including among children living within informal settlements.

Funding

Bill & Melinda Gates Foundation; Gavi, the Vaccine Alliance.

Evaluation strategies for measuring pneumococcal conjugate vaccine impact in low-resource settings

OBJECTIVES

Pneumococcal conjugate vaccines (PCVs) are effective in reducing pneumococcal disease. We measured 13-valent PCV (PCV13) effect on different pneumococcal outcomes using diverse studies in Lao People's Democratic Republic.

METHODS

Studies included: pre-PCV13 population-based record review of hospitalized childhood pneumonia cases; acute respiratory infection (ARI) study post-PCV13 to demonstrate effectiveness (VE) against hypoxic pneumonia; invasive pneumococcal disease (IPD) surveillance in all ages (2004-2018); carriage studies in children hospitalized with ARI (2013-2019); community carriage surveys pre- and post-PCV13.

RESULTS

Annual pneumonia incidence rate in children pre-PCV13 was 1,530 (95% confidence interval [CI] 1,477-1,584) per 100,000. Adjusted VE against hypoxic pneumonia was 37% (95% CI 6-57%). For IPD, 85% (11/13) of cases were due to vaccine-types pre-PCV13, and 43% (3/7) post-PCV13 in children aged <5 years; for ≥5 years, 61% (27/44) and 42% (17/40), respectively. For ARI cases, adjusted VE for vaccine-type carriage was 39% (95% CI 4-60) in <5 year olds; slightly higher than community surveys (23% [95% CI 4-39%] in 12-23 month olds).

CONCLUSIONS

Despite limited baseline data, we found evidence of PCV13 impact on disease and carriage. Our approach could be used in similar settings to augment existing WHO PCV evaluation guidelines.

Australia's Role in Pneumococcal and Human Papillomavirus Vaccine Evaluation in Asia-Pacific

Australian researchers have made substantial contributions to the field of vaccinology over many decades. Two examples of this contribution relate to pneumococcal vaccines and the human papillomavirus (HPV) vaccine, with a focus on improving access to these vaccines in low- and lower-middle-income countries (LLMICs). Many LLMICs considering introducing one or both of these vaccines into their National Immunisation Programs face significant barriers such as cost, logistics associated with vaccine delivery. These countries also often lack the resources and expertise to undertake the necessary studies to evaluate vaccine performance. This review summarizes the role of Australia in the development and/or evaluation of pneumococcal vaccines and the HPV vaccine, including the use of alternative vaccine strategies among countries situated in the Asia-Pacific region. The outcomes of these research programs have had significant global health impacts, highlighting the importance of these vaccines in preventing pneumococcal disease as well as HPV-associated diseases.

Lack of effectiveness of 13-valent pneumococcal conjugate vaccination against pneumococcal carriage density in Papua New Guinean infants

BACKGROUND

Papua New Guinea (PNG) introduced the 13-valent pneumococcal conjugate vaccine (PCV13) in 2014, with administration at 1, 2, and 3 months of age. PCV13 has reduced or eliminated carriage of vaccine types in populations with low pneumococcal carriage prevalence, carriage density and serotype diversity. This study investigated PCV13 impact on serotype-specific pneumococcal carriage prevalence, density, and serotype diversity in PNG infants, who have some of the highest reported rates of pneumococcal carriage and disease in the world.

METHODS

Nasopharyngeal swabs were collected at 1, 4 and 9 months of age from PCV13-vaccinated infants (n = 57) and age-/season-matched, unvaccinated infants (at approximately 1 month, n = 53; 4 months, n = 57; 9 months, n = 52). Serotype-specific pneumococcal carriage density and antimicrobial resistance genes were identified by qPCR and microarray.

RESULTS

Pneumococci were present in 89% of swabs, with 60 different serotypes and four non-encapsulated variants detected. Multiple serotype carriage was common (47% of swabs). Vaccine type carriage prevalence was similar between PCV13-vaccinated and unvaccinated infants at 4 and 9 months of age. The prevalence of non-vaccine type carriage was also similar between cohorts, with non-vaccine types present in three-quarters of samples (from both vaccinated and unvaccinated infants) by 4 months of age. The median pneumococcal carriage density was high and similar at each age group (~7.0 log₁₀genome equivalents/mL). PCV13 had no effect on overall pneumococcal carriage density, vaccine type density, non-vaccine type density, or the prevalence of antimicrobial resistance genes.

CONCLUSION

PNG infants experience dense and diverse pneumococcal colonisation with concurrent serotypes from 1 month of age. PCV13 had no impact on pneumococcal carriage density, even for vaccine serotypes. The low prevalence of vaccine serotypes, high pneumococcal carriage density and abundance of non-vaccine serotypes likely contribute to the lack of PCV13 impact on carriage in PNG infants. Indirect effects of the infant PCV programs are likely to be limited in PNG. Alternative vaccines with broader coverage should be considered.

A Narrative Review of Pneumococcal Disease in Children in the Philippines

This narrative review describes the epidemiology of invasive pneumococcal diseases, nasopharyngeal carriage, and antibiotic resistance of Streptococcus pneumoniae serotypes, and vaccination coverage in children in the Philippines. Epidemiological data show that, despite the availability of the free-of-cost 13-valent pneumococcal conjugate vaccine for infants as part of the National Immunization Program, the burden of pneumococcal disease in young children remains high in the Philippines. The significant variability in data reported between studies highlights an urgent need for active and comprehensive disease surveillance for more accurate estimates of pneumococcal disease in the country. Although data from 2001 to 2013 show high rates of pneumococcal carriage in children in the Philippines aged < 5 years, contemporary data are lacking, again emphasizing the need for active surveillance programs. The introduction of pneumococcal conjugate vaccines has resulted in substantial declines in disease caused by pneumococcal serotypes included in the vaccines, but the emergence of pneumococcal disease due to nonvaccine serotypes is an ongoing concern. Surveillance of actively circulating serotypes is critical to better understand vaccine coverage. Antimicrobial resistance of S. pneumoniae remains a significant threat to public health worldwide; data regarding antibiotic resistance in young children in the Philippines are limited, but reports generally show low rates of antibiotic resistance in this group. National immunization rates have increased in recent years, yet many individuals are still unprotected from pneumococcal disease. Overall, there is a critical need for contemporary and accurate disease surveillance in the Philippines. Such data would provide better estimates of pneumococcal disease incidence, serotype distribution, and antibiotic resistance to better inform vaccination strategies and to ensure that children in the Philippines are best protected against pneumococcal disease.

Direct and indirect effect of 10 valent pneumococcal vaccine on nasopharyngeal carriage in children under 2 years of age in Matiari, Pakistan

Background

Pakistan introduced Ten-valent pneumococcal-conjugate-vaccine PCV10 in 2012 as a 3 + 0 schedule without catch-up.

Methods

Children <2 years old in Matiari, Sindh provided nasopharyngeal swabs between 2014 and 2018, which were cultured for pneumococcus and serotyped through multiplex PCR at the Aga Khan University Hospital. Carriage rates over time for Vaccine-Type (VT) and Non-VT (NVT) serotypes were used to estimate direct, indirect, total and overall effects of vaccination. Regression analysis was used to determine factors associated with VT carriage.

Results

Pneumococcus was detected in 2370/3140 (75%). VT carriage decreased overall, 16.1–9.6% (p-trend <0.001); vaccinated (all 3 doses of PCV10 received) 11.3–8.1% (p-trend 0.031) and unvaccinated (no PCV10 dose received) 17.4–10.3% (p-trend 0.003) with a decline in serotypes 6B, 9V/9A and 19F. Immunization increased from 41.0% to 68.4% (p-trend 0.001). Direct effect of vaccine was 32.8% (95% CI 14.7–47.0%) and indirect effect 44.6%(95% CI 40.6–48.6%). Factors associated with decreased VT colonization were education 1–5 years (aOR 0.7, 95%CI 0.6–1.0), history of difficulty breathing (aOR 0.7, 95%CI 0.5–1.0), exposure to smoke (aOR 0.8, 95% CI 0.6–1.0), child fully immunized (aOR 0.7, 95%CI 0.5–1.0) and enrolled in 3rd (aOR 0.6, 95%CI 0.4–0.8) and 4th (aOR 0.6, 95%CI 0.5–0.9) year of the study whereas history of runny nose (aOR 1.5, 95% CI 1.2–1.9) was positively associated.

Conclusions

Decrease in VT pneumococcal carriage in vaccinated and unvaccinated children indicates herd immunity. Sustained increase in vaccine coverage and close long-term surveillance is warranted.

Epidemiology, Nasopharyngeal Carriage, Serotype Prevalence, and Antibiotic Resistance of Streptococcus pneumoniae in Indonesia

In Indonesia, pneumococcal disease represents a considerable public health concern; however, published data on the epidemiology, nasopharyngeal carriage, serotype prevalence, and antibiotic resistance of Streptococcus pneumoniae in this region are limited. Therefore, this article reviews the available data from a variety of sources and also summarizes pneumococcal conjugate vaccine implementation and recommendations in Indonesia and subsequent impact on pneumococcal disease. Regional pneumococcal vaccination recommendations in Asia were also reviewed. Studies showed that pneumococcal nasopharyngeal carriage prevalence in Indonesia was approximately 43% to 55% in healthy children aged less than 5 years, which varied by age group, region, and year. Serotype analysis of pneumococcal nasopharyngeal carriage isolates in Indonesia revealed that 38% to 60% of isolates would be covered by the 13-valent pneumococcal conjugate vaccine (PCV13). The antimicrobial resistance of pneumococcal disease has increased over time; between 1997 and 2012, resistance to penicillin and sulfamethoxazole increased from 0% to 28% and 9% to 62%, respectively. Inclusion of pneumococcal conjugate vaccines into immunization programs is being implemented gradually. In 2017, Indonesia implemented a regional PCV13 immunization program in Lombok with a 2 + 1 vaccination schedule that was expanded in 2018-2019 to West Nusa Tenggara and Bangka Belitung Provinces; this expansion is predicted to substantially reduce the burden of pneumococcal disease in Indonesia. Overall, the limited data available regarding pneumococcal disease in Indonesia highlight the unmet need for comprehensive disease surveillance studies in this region that can help direct vaccination strategies.

Pneumococcal disease in Thailand

This review examines the epidemiology of pneumococcal disease, serotype prevalence, antibiotic resistance, and national vaccination recommendations in Thailand. The incidence of invasive pneumococcal disease (IPD) and annualized hospitalization rates for pneumococcal bacteremia in Thailand were highest in children aged <5years and the elderly. The most prevalent serotype is serotype 6B, which is included in both the 10- and 13-valent pneumococcal conjugate vaccines (PCV10 [also known as PHiD-CV] and PCV13, respectively) registered in Thailand. Other common serotypes are 14, 18C, 19F, and 23F (included in both PCVs) and 6A and 19A (only included in PCV13). PCV10/PHiD-CV and PCV13 should cover 48.8%-74% and 73.2%-92% of isolates among children aged ≤5 years, respectively, and 40.0%-47.9% and 58.3%-60.9% of isolates among adults aged ≥65 years. Only PCV13 is licensed for adults in Thailand. Pneumococcal isolates were most commonly resistant to erythromycin, cefuroxime, and penicillin. Despite their demonstrated cost effectiveness and efficacy in reducing nasopharyngeal carriage and IPD, PCVs are not included in the Thai national immunization program. The serotype-specific IPD incidence in Thailand suggests that PCVs will reduce the disease burden in all age groups, but particularly in children and older adults.

Factors associated with pneumococcal carriage and density in infants and young children in Laos PDR

Nasopharyngeal carriage of Streptococcus pneumoniae (the pneumococcus) is a precursor to pneumococcal disease. Several host and environmental factors have been associated with pneumococcal carriage, however few studies have examined the relationship between host factors and pneumococcal carriage density. We sought to identify risk factors for pneumococcal carriage and density using data from cross-sectional pneumococcal carriage surveys conducted in the Lao People's Democratic Republic before and after the introduction of the 13-valent pneumococcal conjugate vaccine (PCV13). Nasopharyngeal swabs were collected infants from aged 5–8 weeks old (n = 999) and children aged 12–23 months (n = 1,010), pneumococci detected by quantitative PCR, and a risk factor questionnaire completed. Logistic and linear regression models were used to evaluate associations between participant characteristics and pneumococcal carriage and density. In infants aged 5–8 weeks, living in a household with two or more children under the age of five years (aOR 1.97; 95% CI 1.39–2.79) and low family income (aOR 1.64; 95% CI 0.99–2.72) were positively associated with pneumococcal carriage. For children aged 12–23 months, upper respiratory tract infection (URTI) symptoms (aOR 2.64; 95% CI 1.97–3.53), two or more children under five in the household (aOR 2.40; 95% CI 1.80–3.20), and rural residence (aOR 1.84, 95% CI 1.35–2.50) were positively associated with pneumococcal carriage. PCV13 vaccination was negatively associated with carriage of PCV13 serotypes (aOR 0.60; 95% CI 0.44–0.83). URTI symptoms (p < 0.001), current breastfeeding (p = 0.005), rural residence (p = 0.012), and delivery by Caesarean section (p = 0.035) were associated with higher mean pneumococcal density in pneumococcal carriers (both age groups combined). This study provides new data on pneumococcal carriage and density in a high disease burden setting in southeast Asia.

Using pneumococcal carriage studies to monitor vaccine impact in low- and middle-income countries

Pneumococcal disease is a leading cause of childhood mortality, globally. The pneumococcal conjugate vaccine (PCV) has been introduced to many countries worldwide. However there are few studies evaluating PCV impacts in low- and middle-income countries (LMIC) because measuring the impact of PCV on pneumococcal disease in LMICs is challenging. We review the role of pneumococcal carriage studies for the evaluation of PCVs in LMICs and discuss optimal methods for conducting these studies. Fifteen carriage studies from 13 LMICs quantified the effects of PCV on carriage, and identified replacement carriage serotypes in the post-PCV era. Ten studies reported on the indirect effects of PCV on carriage. Results can be used to inform cost-effectiveness evaluations, guide policy decisions on dosing and product, and monitor equity in program implementation. Critically, we highlight gaps in our understanding of serotype replacement disease in LMICs and identify priorities for research to address this gap.