Stefan Flasche, United Kingdom

LSHTM IDE

Presenter Of 1 Presentation

ESTIMATING THE CONTRIBUTION OF DIFFERENT AGE STRATA TO VACCINE SEROTYPE PNEUMOCOCCAL TRANSMISSION IN THE PRE VACCINE ERA, A MODELLING STUDY (ID 411)

Session Name
Population Sciences - Epidemiology, Economics, and Mathematical Modelling

Abstract

Background

Herd protection has contributed greatly to PCV impact and may enable use of reduced dose schedules. We estimated which population age groups contribute most to VT pneumococcal transmission and hence herd effects

Methods

We used transmission models to mirror pre PCV epidemiology in England & Wales, Finland, Kilifi in Kenya and Nha Trang in Vietnam and extracted the per capita and population based contribution of different age groups to VT transmission.

Results

<1y old infants cause frequent secondary vaccine type infections per capita. However, 1-5y olds have the much higher contribution to the force of infection at 51%(28-73), 40%(27-59), 37%(28-48) and 67%(41-86) of the total infection pressure in E&W, Finland, Kilifi and Nha Trang, respectively. Unlike the other settings, school age children in Kilifi were the dominant source for VT infections with 42% (29-54) of all infections caused. Similarly, the main source of VT infections in infants are pre-school children and in Kilifi 39%(28-51) of VT infant infections stem from school age children, whereas this was below 15% in the other settings.

Conclusions

Pre-school children are key PCV targets for achieving herd immunity. In highly endemic settings school children may substantially contribute to transmission and may have little PCV protection with current schedules.

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Author Of 5 Presentations

PHYLOGENETIC INFERENCE OF THE TRANSMISSION DIRECTION OF PNEUMOCOCCAL INFECTION, A VALIDATION STUDY (ID 719)

Abstract

Background

Sustaining herd protection via reduced dose schedules may ameliorate pneumococcal conjugate vaccine costs. However, there is limited understanding of pneumococcal transmission pathways and their role in herd immunity. We aimed to develop and validate phylogenetic methods for detecting the occurrence and direction of pneumococcal transmission.

Methods

Based on the timing of serotype-specific carriage within a household, 10 likely transmission pairs and the corresponding transmission direction were identified from a longitudinal study of nasopharyngeal carriage in the UK and sequenced by whole genome sequencing. Any metadata were blinded, and linkage and the transmission direction inferred from the genomic data alone using Phyloscanner.

Results

Unblinding revealed that transmission pair linkage via genomics was identical to that based on epidemiological criteria. One instance of co-colonization was detected and only the dominant serotype was transmitted. All transmission pairs had moderate to strong phylogenetic signals suggesting transmission direction, however, only 6/10 directions were concordant with the epidemiological metadata.

Conclusions

Phylogenetics did successfully predict transmission pairs in this small sample. To improve the inference of transmission direction we will consider factors including sequencing coverage, degrees of intra-host diversity, and phylogenetic uncertainty, although concordance with epidemiolocal metadata may be limited by imperfect sensitivity of culture-based tests for pneumococcal detection.

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PREDICTING THE IMPACT OF PCV13 ON INVASIVE PNEUMOCOCCAL DISEASE (IPD) IN MAINLAND CHINA (ID 823)

Abstract

Background

China is one of few countries yet to introduce PCV. We aimed to estimate the long-term impact of a PCV13 programme on childhood IPD in mainland China, accounting for provincial heterogeneity.

Methods

A Bayesian hierarchical model was fit to systematic review data on the proportion of vaccine-type IPD and carriage in each province. A mechanistic model was then used to predict the relative reduction in IPD incidence of a PCV13 programme, assuming VT circulation is eventually interrupted and replaced by NVTs.

Results

Across China, we estimate that a median 75% (95% HDI: 53 – 90%) of carriage and 88% (95% HDI: 76 - 94%) of IPD is caused by vaccine serotypes. A mature PCV programme would lead to a median 51% (95% HDI: -40 – 81%) reduction in the incidence of IPD, ranging from 33% in Hubei (95% HDI: -34 – 76%) to a median 76% in Beijing (95% HDI: 44 – 92%). All 95% credible intervals for province-level covariate effects contain zero for VT carriage and IPD, and as such the impact estimates in provinces with little or no serotype distribution data remain uncertain.

Conclusions

PCV13 has the potential to substantially reduce the pneumococcal disease burden in China, but data to underpin the estimates is sparse in Western China.

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ESTIMATING THE CONTRIBUTION OF DIFFERENT AGE STRATA TO VACCINE SEROTYPE PNEUMOCOCCAL TRANSMISSION IN THE PRE VACCINE ERA, A MODELLING STUDY (ID 411)

Session Name
Population Sciences - Epidemiology, Economics, and Mathematical Modelling

Abstract

Background

Herd protection has contributed greatly to PCV impact and may enable use of reduced dose schedules. We estimated which population age groups contribute most to VT pneumococcal transmission and hence herd effects

Methods

We used transmission models to mirror pre PCV epidemiology in England & Wales, Finland, Kilifi in Kenya and Nha Trang in Vietnam and extracted the per capita and population based contribution of different age groups to VT transmission.

Results

<1y old infants cause frequent secondary vaccine type infections per capita. However, 1-5y olds have the much higher contribution to the force of infection at 51%(28-73), 40%(27-59), 37%(28-48) and 67%(41-86) of the total infection pressure in E&W, Finland, Kilifi and Nha Trang, respectively. Unlike the other settings, school age children in Kilifi were the dominant source for VT infections with 42% (29-54) of all infections caused. Similarly, the main source of VT infections in infants are pre-school children and in Kilifi 39%(28-51) of VT infant infections stem from school age children, whereas this was below 15% in the other settings.

Conclusions

Pre-school children are key PCV targets for achieving herd immunity. In highly endemic settings school children may substantially contribute to transmission and may have little PCV protection with current schedules.

Hide