Periodic cycles of pneumococcal serotypes carried by children before and after 7-valent pneumococcal conjugate vaccine

Streptococcus pneumoniae carriage studies in adults: Importance, challenges, and key issues to consider when using quantitative PCR-based approaches

Streptococcus pneumoniae causes significant morbidity and mortality among older adults. Detection of pneumococcal carriage is an accepted endpoint in pneumococcal conjugate vaccine studies. However, low sensitivity of culture-based approaches and nasopharyngeal samples have hampered adult S. pneumoniae carriage studies in the past. In contrast, detection of adult S. pneumoniae carriers with qPCR-based approaches can achieve high sensitivity and specificity and qPCR-based testing of oral samples improves accuracy of adult carriage detection. In this Viewpoint we outline a strategy for accurate qPCR-based testing. We recommend a dual-target approach for S. pneumoniae qPCR detection as no genetic target is universally present among or solely unique to it. Furthermore, we advise the evaluation of concordance among quantified qPCR targets to improve the accuracy of S. pneumoniae testing and qPCR-based serotyping. We do not recommend omission of qPCR-based oral sample testing as it will likely result in an underestimation of true adult carrier rates.

Evidence for the intermediate disturbance hypothesis and exponential decay in replacement in Streptococcus pneumoniae following use of conjugate vaccines

Understanding how pneumococci respond to pneumococcal conjugate vaccines (PCVs) is crucial to predict the impact of upcoming higher-valency vaccines. However, stages in pneumococcal community succession following disturbance are poorly understood as long-time series on carriage are scarce and mostly evaluated at end-point measurements. We used a 20-year cross-sectional dataset of pneumococci carried by Portuguese children, and methods from community ecology, to study community assembly and diversity following use of PCV7 and PCV13. Two successional stages were detected upon introduction of each PCV: one in which non-vaccine serotypes increased in abundance, fitted by a broken-stick model, and a second in which the community returned to the original structure, fitted by a geometric series, but with different serotype profile and a drop in richness as great as 24%. A peak in diversity was observed for levels of intermediate vaccine uptake (30–40%) in agreement with the intermediate disturbance hypothesis. Serotype replacement was fitted by an exponential decay model (R² = 80%, P < 0.001). The half-life for replacement was 8 years for PCV7 and 10 years for PCV13. The structure of the pneumococcal community is resilient to vaccine pressure. The increasing loss of diversity, however, suggests it could eventually reach a threshold beyond which it may no longer recover.

Impact of private use of the 13-valent pneumococcal conjugate vaccine (PCV13) on pneumococcal carriage among Portuguese children living in urban and rural regions

In Portugal, the 13-valent pneumococcal conjugate vaccine (PCV13) was commercially available between 2010 and 2015, following a decade of private use of PCV7. We evaluated changes on serotype distribution and antimicrobial susceptibility of pneumococci carried by children living in two regions of Portugal (one urban and one rural). Three epidemiological periods were defined: pre-PCV13 (2009-2010), early-PCV13 (2011-2012), and late-PCV13 (2015-2016). Nasopharyngeal samples (n = 4,232) were obtained from children 0-6 years old attending day-care centers. Private use of PCVs was very high in both regions (>75%). Pneumococcal carriage remained stable and high over time (62.1%, 62.4% and 61.6% (p = 0.909) in the urban region; and 59.8%, 62.8%, 59.5% (p = 0.543) in the rural region). Carriage of PCV7 serotypes remained low (5.3%, 7.8% and 4.3% in the urban region; and 2.5%, 3.7% and 4.8% in the rural region). Carriage of PCV13 serotypes not targeted by PCV7 decreased in both the urban (16.4%, 7.3%, and 1.6%; p < 0.001) and rural regions (13.2%, 7.8%, and 1.9%; p < 0.001). This decline was mostly attributable to serotype 19A (14.1%, 4.4% and 1.3% in the urban region; and 11.1%, 3.6% and 0.8% in the rural region, both p < 0.001). Serotype 3 declined over time in the urban region (10.1%, 4.4%, 0.8%; p < 0.001) and had no obvious trend in the rural region (4.2%, 6.7%, 2.4%; p = 0.505). Serotype 6C decreased in both regions while serotypes 11D, 15A/B/C, 16F, 21, 22F, 23A/B, 24F, 35F, and NT were the most prevalent in the late-PCV13 period. Intermediate resistance to penicillin and non-susceptibility to erythromycin decreased significantly in both regions (19.5%, 13.3%, and 9.3%; and 25.4%, 25.9%, and 13.4%; both p < 0.001, respectively in the urban region; and 12.4%, 11.1%, and 2.8% (p < 0.001); and 15.3%, 14.7%, and 9.2% (p = 0.037), respectively, in the rural region). In conclusion, private use of PCV13 led to significant changes on the pneumococcal population carried by children in Portugal.

Differences in the Impact of Pneumococcal Serotype Replacement in Individuals With and Without Underlying Medical Conditions

BACKGROUND

Pneumococcal conjugate vaccines (PCVs) have had a well-documented impact on the incidence of invasive pneumococcal disease (IPD). However, declines in IPD due to vaccine-targeted serotypes have been partially offset by increases in IPD due to nonvaccine serotypes (NVTs). The goal of this study was to quantify serotype-specific changes in the incidence of IPD that occurred in different age groups, with or without certain comorbidities, following the introduction of 7-valent pneumococcal conjugate vaccine (PCV7) and 13-valent pneumococcal conjugate vaccine (PCV13) in the childhood vaccination program in Denmark.

METHODS

We used nationwide surveillance data for IPD and a hierarchical Bayesian regression framework to estimate changes in the incidence of IPD associated with the introduction of PCV7 (2007) and PCV13 (2010) while controlling for serotype-specific epidemic cycles and unrelated secular trends.

RESULTS

Following the introduction of PCV7 and PCV13 in children, the net impact of serotype replacement varied considerably by age group and comorbidities. Differences in the magnitude of serotype replacement were due to variations in the incidence of NVTs in the different risk groups before the introduction of PCVs. The relative increases in the incidence of IPD caused by specific NVTs did not differ appreciably between risk groups in the postvaccination period. Serotype replacement offset a greater proportion of the benefit of PCVs in strata in which the NVTs comprised a larger proportion of cases prior to the introduction of the vaccines.

CONCLUSIONS

These findings could help to predict the impact of next-generation PCVs in specific risk groups.

Nasopharyngeal pneumococcal carriage in healthy Turkish children after 13-valent conjugated pneumococcal vaccine implementation in the national immunization program

BACKGROUND

In Turkey, pneumococcal conjugated vaccine (PCV) was introduced to the national immunization program as PCV7 in 2008, and was replaced with PCV13 in 2011. The aims of this study were to investigate the effects of PCV13 on nasopharyngeal pneumococcal carriage (NPC) by determining the serotype distribution, and to identify risk factors for carriage, in healthy Turkish children.

METHODS

This prospective study was conducted on 500 healthy children aged 0-13 years between April and November 2014. Nasopharyngeal swab samples were taken, and molecular method for capsular serotyping was performed by multiplex PCR.

RESULTS

Of 500 children, 43.4% were unvaccinated with a PCV (7- or 13-valent), 56.6% were vaccinated and The NPC rate was found to be 9.8%. Of 49 positive Streptococcus pneumoniae isolates, 26 (53%) were PCV13 vaccine strains (VSs), and 17 (34.7%) were non-VS. Six isolates (12.2%) were not typeable by the method applied. The most common serotypes detected were serotype 3 (18.3%), serotype 19F (14.2%), serotype 6A/B (8.1%), serotype 11A (8.1%), and serotype 15B (8.1%). The total coverage rate of the PCV13 serotypes was 60.4%.

CONCLUSION

A significant decrease in carriage rate was detected within three years after the introduction of PCV13 in Turkey. However, the nasopharyngeal carriage of PCV13 strains was found to be interestingly high.

Dominance of vaccine serotypes in pediatric invasive pneumococcal infections in Portugal (2012-2015)

We evaluated the impact of continued 13-valent pneumococcal conjugate vaccine (PCV13) use in the private market (uptake of 61%) in pediatric invasive pneumococcal disease (pIPD) in Portugal (2012–2015). The most frequently detected serotypes were: 3 (n = 32, 13.8%), 14 (n = 23, 9.9%), 1 (n = 23, 9.9%), 7F (n = 15, 6.4%), 19A (n = 13, 5.6%), 6B and 15B/C (both n = 12, 5.2%), and 24F, 10A and 12B (all with n = 10, 4.3%). Taken together, non-PCV13 serotypes were responsible for 42.2% of pIPD with a known serotype. The use of PCR to detect and serotype pneumococci in both pleural and cerebrospinal fluid samples contributed to 18.1% (n = 47) of all pIPD. Serotype 3 was mostly detected by PCR (n = 21/32, 65.6%) and resulted from a relevant number of vaccine failures. The incidence of pIPD varied in the different age groups but without a clear trend. There were no obvious declines of the incidence of pIPD due to serotypes included in any of the PCVs, and PCV13 serotypes still accounted for the majority of pIPD (57.8%). Our study indicates that a higher vaccination uptake may be necessary to realize the full benefits of PCVs, even after 15 years of moderate use, and highlights the importance of using molecular methods in pIPD surveillance, since these can lead to substantially increased case ascertainment and identification of particular serotypes as causes of pIPD.

Expansion of the multidrug-resistant clonal complex 320 among invasive Streptococcus pneumoniae serotype 19A after the introduction of a ten-valent pneumococcal conjugate vaccine in Brazil

BACKGROUND

In 2010, a ten-valent pneumococcal conjugate vaccine (PCV10) was introduced in the routine infant national immunization program in Brazil. Invasive pneumococcal disease (IPD) caused by serotype 19A (Spn19A) increased after the introduction of PCVs in several countries. We compared the frequency, antimicrobial resistance and molecular patterns of invasive Spn19A strains before and after PCV10 introduction in Brazil using data from the national laboratory-based surveillance.

METHODS

We analyzed invasive Spn19A strains isolated from 2005-2009 (pre-PCV10 period), 2011-2015 and 2016-2017 (post-PCV10 periods). Antimicrobial susceptibility was performed for all Spn19A strains, and multilocus sequence typing (MLST) was performed for strains isolated in the age groups <5 years and ≥50 years.

RESULTS

Among the study period, a total of 9,852 invasive Spn strains were analyzed, and 673 (6.8%) belonged to serotype 19A. Overall, the proportion of Spn19A among the total number of IPD strains increased from 2.8% in 2005-2009 to 7.0% and 16.4% in 2011-2015 and 2016-2017, respectively. The relative increase in Spn19A was observed especially in children <5 years old (2005-2009: 3.2%; 2011-2015: 15.5%; 2016-2017: 31.2%). The percentage of penicillin resistance (MIC 2.0-4.0 μg/mL), erythromycin resistance and multidrug resistance (MDR) increased after PCV10 introduction due to the expansion of the MDR clonal complex CC320 (2005-2009: 8.6%; 2011-2015: 56.1%; 2016-2017: 66.5%).

CONCLUSION

We observed an expansion of MDR-CC320 among invasive Spn19A strains after PCV10 introduction in Brazil, probably related to a combination of factors, such as vaccination and antimicrobial pressure. Continued surveillance of Spn19A strains is necessary to monitor the sustainability of this clonal complex in the Brazilian population.

Pneumococcal carriage in children and their household contacts six years after introduction of the 13-valent pneumococcal conjugate vaccine in England

Background

In April 2010, 13-valent pneumococcal conjugate vaccine (PCV13) replaced PCV7 in the infant immunisation schedule in England and Wales. Despite limited serotype replacement in invasive pneumococcal disease (IPD) during the first four post-PCV13 years, non-vaccine type (NVT) IPD increased substantially in 2014/15. We undertook a carriage study in 2015/16 to help understand the reasons for this increase.

Methods and findings

Families with a child aged <5 years attending a participating general practice in Gloucestershire or Hertfordshire were invited to provide nasopharyngeal swabs from all consenting members. Swabs from 650 individuals (293 under five, 73 five to twenty and 284 >twenty years) were cultured and serotyped for Streptococcus pneumoniae. Results were compared with those from three previous household studies conducted in the same populations between 2001 to 2013, and with the serotypes causing IPD to estimate case-carrier ratios (CCRs). Overall carriage prevalence did not differ between the four carriage studies with reductions in vaccine-type carriage offset by increases in NVT carriage. While no individual NVT serotype showed an increase in CCR from 2012/13, the composition of the serotypes comprising the NVT group differed such that the overall CCR of the NVT group had significantly increased since 2012/13. Carriage of two PCV13 serotypes, 3 and 19A, was found in 2015/16 (3/650 = 0.5% and 2/650 = 0.3% respectively) with no overall reduction in carriage prevalence of PCV13-7 serotypes since 2012/13, though 6C prevalence, a vaccine-related serotype, had reduced from 1.8% in 2012/13 to 2/648 (0.3%) in 2015/16, p = 0.013.

Conclusions

There was continuing evolution in carried NVTs six years after PCV13 introduction which, in addition to being vaccine-driven, could also reflect natural secular changes in certain NVTs. This poses challenges in predicting future trends in IPD. Elimination of carriage and disease due to serotypes 3 and 19A may not be achieved by PCV13.