Seroprevalence of pertussis in The Netherlands: evidence for increased circulation of Bordetella pertussis

Understanding the impact of adult pertussis and current approaches to vaccination: A narrative review and expert panel recommendations

Pertussis has several notable consequences, causing economic burden, increased strain on healthcare facilities, and reductions in quality of life. Recent years have seen a trend toward an increase in pertussis cases affecting older children and adults. To boost immunity, and protect vulnerable populations, an enduring approach to vaccination has been proposed, but gaps remain in the evidence surrounding adult vaccination that are needed to inform such a policy. Gaps include: the true incidence of pertussis and its complications in adults; regional variations in disease recognition and reporting; and incidence of severe disease, hospitalizations, and deaths in older adults. Better data on the efficacy/effectiveness of pertussis vaccination in adults, duration of protection, and factors leading to poor vaccine uptake are needed. Addressing the critical evidence gaps will help highlight important areas of unmet need and justify the importance of adult pertussis vaccination to healthcare professionals, policymakers, and payers.

Immunity of Canadians and risk of epidemics workshop - Conference report

On November 18-19, 2019, the Immunity of Canadians and Risk of Epidemics (iCARE) Network convened a workshop in Toronto, Ontario, Canada. The objectives of the workshop were to raise the profile of sero-epidemiology in Canada, discuss best practice and methodological innovations, and strategize on the future direction of sero-epidemiology work in Canada. In this conference report, we describe the presentations and discussions from the workshop, and comment on the impact of the COVID-19 pandemic on serosurveillance initiatives, both in Canada and abroad.

The association between vaccine hesitancy and pertussis: a systematic review and meta-analysis

BACKGROUND

Robust routine immunization schedules for pertussis-containing vaccines have been applied for years, but pertussis outbreaks remain a worldwide problem. This study aimed to investigate the association between vaccine hesitancy and pertussis in infants and children.

METHODS

We searched PubMed, Cochrane, Web of Science, Embase, and China National Knowledge Internet for studies published between January 2012 and June 2022. This study included case-control and cohort studies that assessed the association between childhood/maternal vaccine hesitancy and odds ratios (ORs), risk ratios (RRs), and vaccine effectiveness (VE) related to pertussis in infants and children [Formula: see text] 9 years old. ORs/VEs with a 95% confidence interval (CI) were calculated. Random-effects meta-analysis models were used for appropriate pooled estimates, and heterogeneity was assessed using [Formula: see text]. Cumulative meta-analysis and subgroup analyses stratified by study characteristics were performed.

RESULTS

Twenty-two studies were included, with a mean quality score of 7.0 (range 6.0-9.0). Infants and children with pertussis were associated with higher vaccine hesitancy to all doses (OR = 4.12 [95% CI: 3.09-5.50]). The highest OR was between children who were unvaccinated over four doses and children who were fully vaccinated (OR = 14.26 [95%CI: 7.62-26.70]); childhood vaccine delay was not statistically significantly associated with pertussis risk (OR = 1.18 [95% CI: 0.74-1.89]). Maternal vaccine hesitancy was associated with significantly higher pertussis risk in infants aged 2 and 3 months old, with higher pertussis ORs in infants [Formula: see text] 2 months old (OR = 6.02 [95%CI: 4.31-8.50], OR = 5.14 [95%CI: 1.95-13.52] for infants [Formula: see text] 2 and [Formula: see text] 3 months old, respectively). Maternal and childhood VEs were high in reducing pertussis infection in infants and children. The administration time of maternal vaccination had little effect on VE.

CONCLUSION

Vaccine hesitancy increased pertussis risks in infants and children. Ensuring that children receive up-to-date pertussis vaccines is essential; short delays in receiving childhood vaccinations may be unimportant. Maternal vaccinations for pertussis should be encouraged.

Maternal vaccination against pertussis as part of the national immunization program: a qualitative evaluation among obstetric care providers one year after the implementation in December 2019

BACKGROUND

Immunization of pregnant women with a tetanus-diphtheria-and-acellular-pertussis (Tdap) vaccine is an effective and safe way to protect infants from pertussis before their primary vaccinations. Vaccine uptake among pregnant women is influenced by their care providers' attitudes toward maternal vaccination. This qualitative study aimed to evaluate the implementation of the maternal Tdap vaccination under the National Immunization Program of the Netherlands from the perspective of obstetric care providers.

METHODS

In this qualitative and explorative study, we conducted in-depth interviews by telephone with obstetric care providers who were selected from a pool of respondents (convenience sampling) to a questionnaire in a previous study. The interviews were based on a semi-structured interview guide that covered three aspects of the implementation strategy: providers' overall experience with the implementation of maternal Tdap vaccination in the Netherlands; implementation logistics and counseling, and pregnant women referrals to municipal Youth Healthcare Centers. The interviews were recorded, pseudonymized and transcribed verbatim. Transcripts were analyzed according to the Thematic Analysis approach by two researchers independently in two phases of iterative coding, categorizing, reviewing and redefining until ultimately, emergent themes regarding maternal Tdap vaccination implementation were identified.

RESULTS

Interviews with 11 midwives and 5 OB-GYN physicians yielded 5 major themes regarding the Tdap vaccination implementation strategy: challenges throughout the implementation process, views on maternal Tdap vaccination, general versus tailored counseling, provider responsibilities in vaccine promotion, and impact of materials for information delivery. Participants indicated that to improve provider attitudes toward Tdap vaccination, its implementation requires clear and transparent information about what is entailed, i.e., what is expected from obstetric care providers, how they can obtain information, and when their actions must be initiated. Participants demanded involvement throughout the implementation planning process. They preferred tailored communication with pregnant women over a generalized approach.

CONCLUSION

This study emphasized the importance of involving all relevant healthcare professionals in planning the implementation of maternal Tdap vaccination. Possible barriers perceived by these professionals should be taken into account in order to improve their attitudes toward vaccination, thus to increase uptake among pregnant women.

Distinct early cellular kinetics in participants protected against colonization upon Bordetella pertussis challenge

BACKGROUNDTo date, only limited data are available on the mechanisms of protection against colonization with Bordetella pertussis in humans.METHODSIn this study, the cellular responses to B. pertussis challenge were monitored longitudinally using high-dimensional EuroFlow-based flow cytometry, allowing quantitative detection of more than 250 different immune cell subsets in the blood of 15 healthy donors.RESULTSParticipants who were protected against colonization showed different early cellular responses compared with colonized participants. Especially prominent for colonization-protected participants were the early expansion of CD36- nonclassical monocytes on day 1 (D1), natural killer cells (D3), follicular T helper cells (D1-D3), and plasma cells (D3). Plasma cell expansion on D3 correlated negatively with the CFU load on D7 and D9 after challenge. Increased plasma cell maturation on D11-D14 was found in participants with seroconversion.CONCLUSIONThese early cellular immune responses following experimental infection can now be further characterized and potentially linked to an efficient mucosal immune response, preventing colonization. Ultimately, their presence may be used to evaluate whether new B. pertussis vaccine candidates are protective against B. pertussis colonization, e.g., by bacterial challenge after vaccination.TRIAL REGISTRATIONClinicalTrials.gov NCT03751514.FUNDINGInnovative Medicines Initiative 2 Joint Undertaking and the EuroFlow Consortium.

Prior exposure to B. pertussis shapes the mucosal antibody response to acellular pertussis booster vaccination

Bordetella pertussis (Bp), the causative agent of pertussis, continues to circulate despite widespread vaccination programs. An important question is whether and how (sub)clinical infections shape immune memory to Bp, particularly in populations primed with acellular pertussis vaccines (aP). Here, we examine the prevalence of mucosal antibodies against non-vaccine antigens in aP-primed children and adolescents of the BERT study (NCT03697798), using antibody binding to a Bp mutant strain lacking aP antigens (Bp_mut). Our study identifies increased levels of mucosal IgG and IgA binding to Bp_mut in older aP-primed individuals, suggesting different Bp exposure between aP-primed birth cohorts, in line with pertussis disease incidence data. To examine whether Bp exposure influences vaccination responses, we measured mucosal antibody responses to aP booster vaccination as a secondary study outcome. Although booster vaccination induces significant increases in mucosal antibodies to Bp in both cohorts, the older age group that had higher baseline antibodies to Bp_ mut shows increased persistence of antibodies after vaccination.

Pertussis toxin neutralizing antibody response after an acellular booster vaccination in Dutch and Finnish participants of different age groups

Pertussis incidence has increased in many countries and the disease occurs among all age groups, suggesting the need for booster immunizations through life. In addition to determining the concentration of anti-pertussis toxin (PT) antibodies, the ability of PT neutralizing antibodies (PTNAs) could be used to assess vaccine responses.

Altogether 258 participants [7–10-year-old (N = 73), 11–15-year-old (N = 85), 20–35-year-old (N = 50) and 60–70-year-old (N = 50)] were included. Sera were collected before, one month, and one year after a single dose of a three pertussis component containing acellular pertussis vaccine. The adolescents were primed in childhood either by acellular or whole-cell vaccination. PTNA titres were determined by a Chinese hamster ovary cell assay and anti-PT IgG/IgA antibody concentrations by multiplex immunoassay.

In all age groups, a significant increase in levels of PTNAs and anti-PT IgG was observed one month after vaccination and remained at least two-fold higher one year post-booster, in comparison to pre-booster. Young adults had the lowest response. The strongest increase in PTNAs was observed in participants who had ≥10 IU/mL concentration of anti-PT IgG antibodies pre-booster. At pre-booster, whole-cell-primed adolescents had higher PTNAs than acellular-primed peers (p = 0.047). One year post-booster, the Finnish whole-cell-primed adolescents had a higher level of PTNAs than acellular-primed adolescents (p = 0.049), however, this was not observed in Dutch adolescents. In conclusion, PTNAs increased after vaccination in all age groups, and the strongest increase was related to the presence of high pre-booster antibodies.

Descriptive Overview of Pertussis Epidemiology Among Older Adults in Europe During 2010–2020

Introduction

Following the introduction of pertussis vaccination during infancy, the age-related demographics of pertussis epidemiology have changed.

Methods

To better understand the pertussis burden (defined here as number of cases and/or incidence rate [IR]) among older adults (OA; at least 50 years of age) in Europe, we collected data on the reported number of cases and IR in this population in Denmark, England and Scotland, Finland, Germany, the Netherlands, Norway and Sweden from 2010 to 2020. Additionally, we collected contextual epidemiological information on surveillance systems, case definitions, laboratory diagnostics and vaccination approaches.

Results

We observed large heterogeneity in the burden among OA between countries: annual IRs ranged from 0.4 (England, 2010) to 54.5 (Norway, 2011) per 100,000 population; 9% (Denmark, 2010) to 45% (England, 2017) of all reported cases occurred in OA. No clear impact of changes in contextual epidemiological information or common trends between countries could be observed, highlighting the need for standardised pertussis surveillance programmes across Europe. The epidemiological trends observed in OA were similar to those observed in 0–4-year-olds.

Conclusion

This analysis showed that B. pertussis continues to circulate among OA in Europe, suggesting that current vaccination strategies are insufficient to decrease the disease burden in all age groups. This may indicate that improved monitoring of pertussis in OA and booster vaccination throughout adulthood are necessary to control the total pertussis burden.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40121-022-00668-y.

Whooping cough is an infectious, vaccine-preventable disease that is primarily serious in unvaccinated infants but can also affect adults (at least 50 years old). While vaccination is well established in children, many countries do not routinely vaccinate older adults. Moreover, whooping cough infections in older adults can be difficult to identify for healthcare professionals because of the atypical and mild nature of symptoms. Consequently, the extent of whooping cough occurrence in this population is underestimated. To better understand the extent of disease occurrence, we studied whooping cough infections in Denmark, England and Scotland, Finland, Germany, the Netherlands, Norway and Sweden from 2010 to 2020. Our study was based on the number of laboratory-confirmed cases reported to relevant institutions. We also assessed whether we could identify links between disease occurrence among older adults and contextual epidemiological information, such as disease monitoring systems, methods used for laboratory confirmation, vaccination schedules and vaccination coverage rates. Our study confirmed that whooping cough affects older adults and disease occurrence follows similar trends to those in 0- to 4-year-old children. Because the contextual epidemiological information differed over time and between countries, we could not establish links with disease occurrence in older adults. These data may provide further evidence to authorities that whooping cough among older adults would be better controlled and its burden more accurately estimated with a reinforced comprehensive approach around vaccination and monitoring. Because adults can also infect children who are not yet fully vaccinated, such an approach might help further control the disease in children.

Long Lasting Antibodies From Convalescent Pertussis Patients Induce ROS Production and Bacterial Killing by Human Neutrophils

Pertussis is a respiratory infection caused by the Gram-negative bacterium Bordetella pertussis. Despite high vaccination coverage this disease remains a public health concern worldwide. A better understanding of the protective immune responses to B. pertussis is required for the development of improved vaccines. The aim of this study was to determine the production of reactive oxygen species (ROS) by human neutrophils in response to B. pertussis and to determine the contribution of opsonizing antibodies from convalescent pertussis patients in this response. The serum samples from convalescent patients were taken at <3, 9, 18 and 36 months after diagnosis of pertussis. Also included were sera from healthy age-matched controls. We show that neutrophils produced high levels of ROS in response to opsonized, compared to non-opsonized, B. pertussis and that this effect was independent of the time the convalescent serum samples were taken. This indicates the presence of functional opsonizing antibodies up to 3 years after B. pertussis infection. While opsonization of B. pertussis with serum samples from uninfected controls also induced ROS production, sera from infected individuals induced significantly higher ROS levels. Spearman correlations analysis showed that IgG antibodies targeting fimbriae3 followed by pertactin, and BrkA correlate with ROS production. Additionally, we observed that neutrophils killed opsonized B. pertussis in a ROS-dependent manner. Searching for other antigen-specific antibodies from convalescent pertussis patients involved in ROS production by neutrophils may assist in the identification of novel antigens to improve the current pertussis vaccines.

Association Between Real-time Polymerase Chain Reaction Cycle Threshold Value and Clinical Severity in Neonates and Infants Infected With Bordetella pertussis

BACKGROUND

Polymerase chain reaction (PCR) is highly sensitive and is thus the standard method for diagnosing pertussis. Real-time PCR is widely used because of its accuracy and the simplicity of the simultaneous cycle threshold (Ct) value, which represents the copy numbers of the target gene. Little is known of the association of Ct value with pertussis severity in neonates and infants.

METHODS

This study determined Ct values in neonates and infants diagnosed with pertussis by real-time PCR using nasopharyngeal samples at Vietnam National Children's Hospital in Hanoi in 2017 and 2019. The association of disease severity and clinical parameters were analyzed using univariate and multivariate analyses.

RESULTS

We evaluated 108 patients with pertussis [median age: 63 days, interquartile range (IQR): 41-92 days]. Only 6/108 (6%) received at least 1 dose of a pertussis-containing vaccine. Among them, 24 (22.2%) had severe disease requiring care in a pediatric intensive care unit, 16 (13.8%) required mechanical ventilation, and 3 (2.6%) died. The median Ct value was lower in patients with severe disease (19.0, IQR: 16.5-22.0, n = 24) than in those without severe disease (25.5, IQR: 20.0-30.0, n = 84) (P = 0.002). Logistic regression analyses demonstrated that PCR Ct value [odds ratio (OR): 1.783, 95% confidence interval (CI): 1.013-3.138, P = 0.045], age (OR: 3.118, 95% CI: 1.643-5.920, P = 0.001), and white blood cell counts (OR: 0.446, 95% CI: 0.261-0.763, P = 0.003) remained significantly associated with severe disease.

CONCLUSIONS

Real-time PCR Ct values for pertussis might be useful as a predictor of severe disease in neonates and infants.

Loop-Mediated Isothermal Amplification Coupled With Nanoparticle-Based Lateral Biosensor for Rapid, Sensitive, and Specific Detection of Bordetella pertussis

Bordetella pertussis is the most frequent causative agent for pertussis, which is a highly contagious disease. Here, we developed a method based on loop-mediated isothermal amplification (LAMP) and nanoparticle-based lateral flow biosensor (LFB) for the timely diagnosis of B. pertussis infections. A set of six primers was designed for LAMP reactions, and the LAMP results were rapidly and visually indicated using LFB. The recommended condition for the B. pertussis LAMP reactions is 40 min at 66°C. Our results confirmed that the LAMP-LFB assay could specifically detect B. pertussis and did not cross-react with non-B. pertussis isolates. The sensitivity of the B. pertussis LAMP-LFB assay was 50 fg per reaction. In particular, 108 nasopharyngeal swab (NPS) samples were collected to evaluate the B. pertussis LAMP-LFB assay, and the results were compared with those of the quantitative PCR (qPCR) method. The positive rates of B. pertussis LAMP-LFB and qPCR were 40.7% and 38.8%, respectively, and the agreement between the LAMP-LFB and qPCR results was 98%, with a kappa value of 0.96. The whole process of LAMP-LFB can be completed within 1 h, which is much shorter than that of qPCR, including about 15 min of rapid DNA extraction, 40 min of LAMP reaction, and within 2 min of the LFB test. Collectively, the B. pertussis LAMP-LFB assay developed in this report offers a new option for the rapid, reliable, and simple diagnosis of B. pertussis infections.

Reduced Bordetella pertussis-specific CD4+ T-Cell Responses at Older Age

Pertussis, a human-specific respiratory infectious disease caused by the Gram-negative bacterium Bordetella pertussis (Bp), remains endemic with epidemic years despite high vaccination coverage. Whereas pertussis vaccines and natural infection with Bp confer immune protection, the duration of protection varies and is not lifelong. Recent evidence indicates a considerable underestimation of the pertussis burden among older adults. Whereas the impact of increasing age on Bp-specific humoral immunity has been demonstrated, little is known on immunosenescence of CD4⁺ T-cell responses in the context of Bp. Here, we aimed to address whether increasing age impacts responsiveness of the Bp-specific CD4⁺ T-cells in the memory pool following a clinically symptomatic pertussis infection in whole cell vaccine-primed pediatric and adult cases. Cytokine and proliferative responses and phenotypical profiles of CD4⁺ T cells specific for Bp antigens at an early and late convalescent timepoint were compared. Responses of various Th cytokines, including IFNγ, were significantly lower in older adults at early and late timepoints post diagnosis. In addition, we found lower frequencies of Bp-specific proliferated CD4⁺ T cells in older adults, in the absence of differences in replication profile. Phenotyping of Bp-specific CD4⁺ T cells suggested reduced expression of activation markers rather than increased expression of co-inhibitory markers. Altogether, our findings show that the magnitude and functionality of the Bp-specific memory CD4⁺ T-cell pool decrease at older age. Declined CD4⁺ T-cell responsiveness to Bp is suggested to contribute to the burden of pertussis in older adults.

More than 10 years after introduction of an acellular pertussis vaccine in infancy: a cross-sectional serosurvey of pertussis in the Netherlands

Background

Pertussis is a respiratory disease and still endemic despite high vaccination coverage. In the Dutch national immunisation programme (NIP) whole cell pertussis (wP) priming vaccines for infants were replaced by acellular pertussis (aP) priming vaccines in 2005. Serosurveillance gives the opportunity to objectively monitor effects of changes in the NIP on infection prevalence and vaccine response in the population over time.

Methods

For this population-based cross-sectional serosurvey a representative sample of Dutch residents (0-89 years) was drawn in 2016/2017. Primary outcome was the percentage of participants with pertussis toxin specific antibody concentrations ≥ 100 IU/ml as an indicator of recent infection, and to identify groups possibly more vulnerable to pertussis infection. Percentages were compared with previous results from 2006/2007.

Findings

In total 7621 persons were included in the analysis. An increase in recent infections from 3•5% to 5•9% was found in the population from 7 years and older (n=6013) in 2016/2017 compared with 2006/2007. Most noteworthy increase was seen in 12-18-year-olds who were wP primed and aP boosted.

Interpretation

Infection prevalence is still increasing in the Netherlands inducing a risk of pertussis disease in vulnerable (age) groups. Delaying the preschool booster might prolong the period of protection during primary school and thereby possibly protect younger siblings. Extra boosters might be considered for risk populations like older adults and people with (pulmonary) co-morbidities, since they have higher chances of complications and hospitalisation.

An unedited Dutch translation of the abstract is available in Supplementary text 1: Nederlandse samenvatting.

Funding

The Dutch Ministry of Health, Welfare, and Sport.

Bordetella pertussis in School-Age Children, Adolescents and Adults: A Systematic Review of Epidemiology and Mortality in Europe

Pertussis (whooping cough) epidemics persist globally despite high vaccine coverage among infants and young children. The resurgence of pertussis in high-income countries is partly due to waning vaccine immunity, resulting in a pool of unprotected adolescents and adults. However, pertussis is generally less severe in adolescents and adults, and this difference in presentation means it can often be unrecognised by healthcare professionals, meaning that it is largely under-diagnosed in older populations. A systematic search of MEDLINE, EMBASE and BIOSIS was undertaken to identify studies published between 1 January 1990 and 17 June 2019, with information on pertussis epidemiology and mortality in school-aged children, adolescents and adults in Europe. A formal statistical comparison (e.g. using meta-analyses) was not possible because of the mix of methodologies reported. There were 69 epidemiological studies and 19 mortality studies identified for review. Over the past decade, the reported incidence of notified pertussis cases varied widely between European countries, which is likely associated with differences in surveillance systems, diagnostic techniques and reporting regulations. However, several studies show that pertussis is circulating among adolescents and adults in Europe, and although pertussis-related morbidity and mortality are highest in infants, there is evidence that adults aged > 50 years are at increased risk. For example, in a hospital-based surveillance study in Portugal, between 2000 and 2015, 94% of hospitalised pertussis cases were infants aged < 1 year, with a case fatality rate (CFR) of 0.8%; however, among hospitalised adult cases of pertussis, the CFRs were 11.5% (aged 18–64 years) and 17.4% (aged > 65 years). Very few European countries currently include pertussis boosters for adults in the national immunisation strategy. In addition to increasing pertussis vaccination coverage in adolescents and adults, mitigation strategies in European countries should include improved diagnosis and treatment in these populations.

Circulation of Bordetella pertussis in the Caribbean Netherlands: a population-based seroepidemiological study

OBJECTIVES

Pertussis is a respiratory infectious disease caused by Bordetella pertussis. In the Caribbean Netherlands (CN), comprising the islands Bonaire, St Eustatius, and Saba, registration of cases is mandatory for disease surveillance. However, insufficient laboratory facilities hamper case confirmation, and circulation persists. The aim of this seroepidemiological study was to gain insight into B. pertussis circulation in CN, and to investigate what factors contribute to the risk of infection.

METHODS

Blood samples and questionnaires were collected for 1829 participants aged 0-90 years. Concentrations of B. pertussis toxin-specific IgG antibodies (anti-Pt) were determined using a bead-based immunoassay to indicate infections within the previous 12 months (based on anti-Pt ≥ 50 IU/mL) in participants without detectable vaccine-induced humoral immunity. Risk factors for recent infection were analyzed using logistic regression models.

RESULTS

An estimated 8.2% (95% CI 6.6-10.1) of CN residents aged ≥ 9 years were found to have been recently infected by B. pertussis. Risk factors for a recent infection were age 12-29 years (13.8-14.6%) and Dutch Caribbean or Surinamese origin (10.7%).

CONCLUSIONS

B. pertussis infections occur frequently among CN residents aged ≥ 9 years, although few clinical pertussis cases are reported. Transmission to vulnerable individuals seems likely and should be taken into account in optimizing vaccination programs.

Retrospective cohort study investigating extent of pertussis transmission during a boarding school outbreak, England, December 2017 to June 2018

On 1 May 2018, a pertussis outbreak was declared and widespread vaccination recommended at an all-female secondary boarding school in southern England. We conducted a retrospective cohort study to determine the extent of pertussis transmission and identify risk factors in this semi-closed population. Of 504 students and staff assessed before post-exposure vaccination, 48% (n = 240) had evidence of pertussis. A sub-analysis of 409 students found that both residential dormitory (p = 0.05) and school year (p = 0.03) were associated with pertussis, with odds decreasing by 11% for each increase in school year (95% confidence interval: 0.7-20.2). Odds of pertussis were 1.7 times higher in those assumed to have received acellular vaccines for their primary course compared with those assumed to have received whole-cell vaccines (based on date of birth), although this difference was not significant (p = 0.12). Our findings support the need for timely, widespread vaccination following identification of cases among adolescents in a semi-closed United Kingdom (UK) setting and to review the evidence for the introduction of an adolescent pertussis booster to the UK routine vaccination programme.

Pertussis seroprevalence among adults of reproductive age (20-39 years) in fourteen European countries

The reported incidence of pertussis in European countries varies considerably. We aimed to study specific Bordetella pertussis seroprevalence in Europe by measuring serum IgG antibody levels to pertussis toxin (anti-PT IgG). Fourteen national laboratories participated in this study including Belgium, Denmark, Finland, Greece, Hungary, Italy, Lithuania, Malta, Norway, Poland, Portugal, Romania, Spain, and Sweden. Each country collected approximately 250 samples (N = 7903) from the age groups 20-29 years (N = 3976) and 30-39 years (N = 3927) during 2010-2013. Samples were anonymous residual sera from diagnostic laboratories and were analyzed at the national laboratories by a Swedish reference method, a commercial ELISA kit, or were sent to Sweden for analysis. The median anti-PT IgG concentrations ranged from 4 to 13.6 IU/mL. The proportion of samples with anti-PT IgG ≥100 IU/mL, indicating a recent infection ranged from 0.2% (Hungary) to 5.7% (Portugal). The highest proportion of sera with anti-PT IgG levels between 50 and <100 IU/mL, indicating an infection within the last few years, was found in Portugal (12.3%) and Italy (13.9%). This study shows that the circulation of B. pertussis is quite extensive in adults, aged 20-39 years, despite well-established vaccination programs in Europe.

Circulation of pertussis and poor protection against diphtheria among middle-aged adults in 18 European countries

Reported incidence of pertussis in the European Union (EU) and the European Economic Area (EEA) varies and may not reflect the real situation, while vaccine-induced protection against diphtheria and tetanus seems sufficient. We aimed to determine the seroprevalence of DTP antibodies in EU/EEA countries within the age groups of 40-49 and 50-59 years. Eighteen countries collected around 500 samples between 2015 and 2018 (N = 10,302) which were analysed for IgG-DTP specific antibodies. The proportion of sera with pertussis toxin antibody levels ≥100 IU/mL, indicative of recent exposure to pertussis was comparable for 13/18 countries, ranging between 2.7-5.8%. For diphtheria the proportion of sera lacking the protective level (<0.1 IU/mL) varied between 22.8-82.0%. For tetanus the protection was sufficient. Here, we report that the seroprevalence of pertussis in these age groups indicates circulation of B. pertussis across EU/EEA while the lack of vaccine-induced seroprotection against diphtheria is of concern and deserves further attention.

Seroprevalence of Bordetella pertussis Infection in Patients With Chronic Obstructive Pulmonary Disease in England: Analysis of the AERIS Cohort

Pertussis is underdiagnosed and underreported in adults and patients with underlying conditions. Patients with chronic obstructive pulmonary disease (COPD) may be at increased risk of severe pertussis. Understanding the true prevalence of pertussis infections in such patients is important. We therefore evaluated the seroprevalence of anti-pertussis toxin (PT) antibodies in a cohort of 40-85-year-old patients diagnosed with moderate, severe or very severe COPD enrolled (between June 2011 and June 2012) in the prospective, observational "Acute Exacerbation and Respiratory InfectionS in COPD" (AERIS; NCT01360398) study, conducted in England. Serum anti-PT antibodies were measured in 104 patients using an enzyme-linked immunosorbent assay on samples collected 12 months (M12) and 24 months (M24) after enrollment. Overall, 14/104 (13.5%) patients had anti-PT concentrations ≥50 IU/mL at M12 or M24, indicative of exposure to Bordetella pertussis during the preceding 2-3 years. Of these, 6/104 (5.8%) had anti-PT ≥70 IU/mL, of whom 3/104 (2.9%) had anti-PT ≥120 IU/mL, indicative of exposure within 12 and 6 months, respectively. These results show a high circulation of B. pertussis in 40-85-year-old patients with moderate, severe or very severe COPD in England between 2012 and 2014, and call for enhanced immunization to prevent pertussis infections in such patients.

Seroepidemiology of pertussis in China: A population-based, cross-sectional study

BACKGROUND

Despite high pertussis vaccination coverage and significant decrease of pertussis since the adoption of the Expanded Programme on Immunization (1978), increased pertussis incidence has been reported in China from 2013 to 2017. This study aimed at evaluating the immune response to pertussis among vaccinated children and beyond in China.

METHODS

The study recruited 2 144 healthy subjects. Serum IgG antibodies against pertussis toxin (anti-PT IgG) were measured by ELISA. Anti-PT IgG concentration (GMC), seropositivity rate (GMC ≥ 40 IU/ml), and recent infection rate (GMC > 100 IU/ml) were calculated. Participants ≤ 2 years-old were further stratified by vaccination schedule intervals and participants ≤ 6 years-old by vaccine used (Domestic DTaP or DTaP-IPV//PRP ~ T (Pentaxim, SP)).

RESULTS

Among 0-6-year-olds, the anti-PT IgG GMC was 5.99 IU/ml (95%CI 5.39-6.67). The GMC increased in accordance with the primary vaccination series (4-6 months) and the toddler booster (18-23 months), and continuously declined thereafter to its nadir at 6 years-old [3.72 IU/ml (95%CI 2.91-4.77)]. GMCs were markedly higher in those vaccinated with DTaP-IPV/PRP ~ T compared to DTaP. In individuals > 6 years-old, the GMC was 5.67 IU/ml (95%CI 5.36-6.00), the seropositivity rate was 6.7% (95%CI 5.5-7.9) and the recent infection rate was 1.2% (95%CI 0.7-1.7). The seropositivity rates increased from 6 years-old and peaked at 9 years-old (10.3% [95%CI 0.7-19.8]).

CONCLUSIONS

Vaccination against pertussis increases anti-PT IgG, but wanes over time. The sero-estimated infection rates increase from school age and peak at about 9 years-old. These results support the addition of a booster of pertussis vaccine at preschool age.

Responses to an acellular pertussis booster vaccination in children, adolescents, and young and older adults: A collaborative study in Finland, the Netherlands, and the United Kingdom

Background

Pertussis can lead to serious disease and even death in infants. Older adults are more vulnerable to complications as well. In high-income countries, acellular pertussis vaccines are used for priming vaccination. In the administration of booster vaccinations to different age groups and target populations there is a substantial between-country variation. We investigated the effect of age on the response to acellular pertussis booster vaccination in three European countries.

Methods

This phase IV longitudinal intervention study performed in Finland, the Netherlands and the United Kingdom between October 2017 and January 2019 compared the vaccine responses between healthy participants of four age groups: children (7–10y), adolescents (11–15y), young adults (20–34y), and older adults (60–70y). All participants received a three-component acellular pertussis vaccine. Serum IgG and IgA antibody concentrations to pertussis antigens at day 0, 28, and 1 year were measured with a multiplex immunoassay, using pertussis toxin concentrations at day 28 as primary outcome. This trial is registered with ClinicalTrialsRegister.eu (2016–003,678–42).

Findings

Children (n = 109), adolescents (n = 121), young adults (n = 74), and older adults (n = 75) showed high IgG antibody concentrations to pertussis toxin at day 28 with GMCs of 147 (95% CI 120–181), 161 (95% CI 132–196), 103 (95% CI 80–133), and 121 IU/ml (95% CI 94–155), respectively. A significant increase in GMCs for vaccine antigens in all age groups by 28 days was found which had decreased by 1 year. Differences in patterns of IgG GMCs at 28 days and 1 year post-vaccination did not have a consistent relationship to age. In contrast, IgA antibodies for all antigens increased with age at all timepoints.

Interpretation

Acellular pertussis booster vaccination induces significant serum IgG responses to pertussis antigens across the age range which are not uniformly less in older adults. Acellular boosters could be considered for older adults to reduce the health and economic burden of pertussis.

[Serological diagnosis of pertussis in older persons.]

The aim of the work was to assess the effectiveness of serodiagnosis of pertussis in people over 50 who complained of prolonged cough. The study included 30 patients over the age of 50 who applied to the consultative diagnostic center complaining of a prolonged cough in the period from 2015 - 2020. Blood serum samples were investigated in enzyme immunoassay with the definition of antitussive antibodies of three classes - IgM, IgG, IgA in the commercial test system RIDASCREEN (R-Biopharm AG, Germany). It was found that in the serum samples of individuals over the age of 50, IgM antibodies above the threshold level were not detected. Patients were divided into two groups - with IgG and IgA antibodies above the threshold level (group 1) and below the threshold level (group 2). In the first group, in 83.3% and 61.1% of patients, the levels of antibodies of the IgG and IgA class significantly exceeded the threshold level (189.8 ± 16.7 U / ml and 290 ± 20 U / ml, respectively), which indicated a pertussis infection; in 5.6% and 38.9% of patients, IgG and IgA class antibodies slightly exceeded the threshold level (20 U / ml and 43 ± 2.3 U / ml, respectively), which indicated a dying infection. In the second group, in 100% of patients, antibodies of the IgM and IgA classes were determined below threshold levels, and IgG antibodies were detected in 58.3% of individuals at low rates, which corresponded to the natural immunological background of individuals not infected with pertussis pathogen. Therefore, in the presence of a prolonged cough in adults, it is advisable to study blood serum samples for the presence of antitussive antibodies of three classes, which is especially important when people of older age live in families with young children and pregnant women.

Is there an association between socioeconomic status and immune response to infant and childhood vaccination in the Netherlands?

INTRODUCTION

Socioeconomic status (SES) is a well-known determinant of health, but its relation with vaccine-induced immunity is less documented. We explored the association between SES and immunoglobulin G (IgG) levels against vaccine-preventable diseases in vaccinated children in the Dutch National Immunization Programme.

METHODS

Data from a population-wide cross-sectional serosurvey in the Netherlands (2006-2007) were used. We compared geometric mean IgG concentrations/titers (GMC/T ratios) against measles, mumps, rubella, Haemophilus influenzae type b (Hib), Neisseria meningococcus type C, diphtheria, tetanus, poliovirus types 1,2,3 and pertussis in children of high versus low SES by linear regression analysis. We included 894 children (0-12 years) at one of two timeframes: 1 month to 1 year, or 1-3 years after vaccination. Mother's educational level and net household income served as binary indicators of SES.

RESULTS

Of 58 possible associations of vaccine-induced antibody responses with educational level and 58 with income, 10 (9%) were statistically significant: 2 favouring (that is, with higher IgG levels at) high educational level (for Hib 1 m-1y after vaccination (GMC/T ratio: 2.99, 95%CI: 1.42-6.30) and polio 2 1 m-1y after the 9-year booster dose (1.14, 1.01-1.27)) and 8 favouring low income (polio 1, 2 and 3 1 m-1y after the 11-month booster (0.74, 0.58-0.94; 0.79, 0.64-0.97; 0.72, 0.55-0.95), polio 3 and pertussis 1-3y after the 11-month booster (0.70, 0.56-0.88; pertussis-prn: 0.60, 0.37-0.98; pertussis-ptx: 0.66, 0.47-0.95), mumps and rubella 1-3y after first vaccination (0.73, 0.55-0.97; 0.70, 0.55-0.90), and rubella 1 m-1y after second vaccination (0.83, 0.55-0.90)). After adjustment for multiple testing, none of the differences remained significant. There was no association between SES and proportion of children with protective IgG levels.

CONCLUSION

In this explorative study, we found no consistent association between SES and immune response to vaccination in the Netherlands and no association with protective IgG levels. Additional studies in other settings should confirm this finding.

Immuno-proteomics analysis between OMV of vaccine and dominant wild type strains of Bordetella pertussis in Iran

BACKGROUND AND OBJECTIVES

Despite widespread vaccination programs against pertussis, there has been a worldwide resurgence of the disease in recent years. We aimed to investigate protein composition of outer membrane vesicles (OMV) of Bordetella pertussis (Bp) and to evaluate the immunogenicity of OMV antigens both in the vaccine and the dominant wild type strains in Iran.

MATERIALS AND METHODS

The OMV were purified from both vaccine and wild type strains. The immunoreactivity of the OMVs was investigated by exposing sera taken from the patients and the vaccinated infants. The protein profiles of OMVs were compared using two-dimensional electrophoresis. The LC-MS/MS was used to analyse and identify differentially expressed protein spots.

RESULTS

The two type strains showed differences in their 2D gel protein profile. Further analysis of selected proteins from the dominant Iranian strains using LC-MS/MS demonstrated that the identified proteins fell into different functional categories including (i) metabolism, (ii) membrane transport and secretion system, (iii) biosynthesis and degradation, (iv) adaption, adhesion, pathogenicity, conserved hypothetical and protection responses. Moreover, a number of immunogenic proteins were identified including Bp 2434 (serine protease) and Bp 1616 (putative DNA binding protein) from the vaccine and the wild type strains, respectively which could be considered as potential antigens for an OMV vaccine.

CONCLUSION

OMV Bp could be considered as an alternative vaccine against pertussis, containing the bacterium's protein antigens that can confer equal efficacy compared to a whole bacterial cell vaccine with advantages such as less side effects and lower costs than acellular pertussis vaccines.

Seroprevalence of Bordetella pertussis toxin antibodies in children and adolescents in Tunis, Tunisia

Pertussis remains a public health concern in most countries. This cross-sectional study aims to investigate the distribution of pertussis toxin antibodies (anti-PT IgG) in Tunisian children and adolescents aged 3–18 years, to define optimal age for booster vaccination. Anti-PT IgG concentrations of enrolled participants were measured using commercial enzyme-linked immunosorbent assay. Concentrations were classified as: indicative of current/recent infection if ⩾100 IU/ml, indicative of recent exposure to Bordetella pertussis within the last year if 40–100 IU/ml and less likely revealing a recent exposure to B. pertussis if <40 IU/ml. Between March and June 2018, a total of 304 participants (mean age: 9.3 years) were included in this study. Overall, 12.8% (95% confidence interval (CI) 9.1%–16.6%) were seropositive (IgG levels ⩾40 IU/ml). Among them, 14.7% (95% CI 2.3%–23.3%) had levels indicative of a current/recent infection. The multivariate Poisson regression analysis suggested associations between female gender, as well as age group 13–18 years and 3–5 years and higher anti-PT IgG concentrations. Our results are consistent with the notion that vaccine-induced immunity decline, as well as circulation of pertussis among school children and adolescents enables them to be reservoirs of infection and disease transmission to vulnerable infants. Booster dose of acellular pertussis vaccine for school entrants is therefore recommended.

A highly sensitive one-tube nested quantitative real-time PCR assay for specific detection of Bordetella pertussis using the LNA technique

OBJECTIVES

Bordetella pertussis is a highly contagious respiratory agent and is the causative pathogen of pertussis, which primarily affects children. Current diagnostic techniques for this pathogen have a variety of limitations including a long culture time, low bacterial load, and lack of specificity.

METHODS

This article reports the development of a one-tube nested quantitative real-time PCR assay using the locked nucleic acid (LNA) technique (LNA-OTN-q-PCR), targeting the BP485 gene and using a simple inexpensive extraction method. A total of 130 clinical samples from patients with clinically suspected pertussis, collected from the Children's Hospital of Hebei, China, were tested by LNA-OTN-q-PCR assay. RT-PCR and two-step semi-nested PCR assays were performed in parallel for comparison.

RESULTS

Only strains of B. pertussis were identified as positive, whereas all of the remaining strains were appropriately identified as negative by the LNA-OTN-q-PCR assay. A single copy per reaction can be detected by the LNA-OTN-q-PCR assay. Additionally, the sensitivity of this method was 100 times that of the RT-PCR assay (100 copies per reaction). Sixty-three of the 130 clinical samples were detected positive by LNA-OTN-q-PCR assay; in contrast, RT-PCR was able to detect only 41 positive samples. Following this, all 63 samples were positively identified by two-step semi-nested PCR. Compared with the two-step semi-nested PCR assay, both the specificity and sensitivity of the LNA-OTN-q-PCR assay using purified DNA and crude extract were 100%.

CONCLUSIONS

This assay was able to detect B. pertussis infection with high sensitivity and specificity. This test shows great potential as a promising technique to detect B. pertussis in both clinical laboratories and public health settings.

Structural mechanism for regulation of DNA binding of BpsR, a Bordetella regulator of biofilm formation, by 6-hydroxynicotinic acid

Bordetella bacteria are respiratory pathogens of humans, birds, and livestock. Bordetella pertussis the causative agent of whopping cough remains a significant health issue. The transcriptional regulator, BpsR, represses a number of Bordetella genes relating to virulence, cell adhesion, cell motility, and nicotinic acid metabolism. DNA binding of BpsR is allosterically regulated by interaction with 6-hydroxynicotinic acid (6HNA), the first product in the nicotinic acid degradation pathway. To understand the mechanism of this regulation, we have determined the crystal structures of BpsR and BpsR in complex with 6HNA. The structures reveal that BpsR binding of 6HNA induces a conformational change in the protein to prevent DNA binding. We have also identified homologs of BpsR in other Gram negative bacteria in which the amino acids involved in recognition of 6HNA are conserved, suggesting a similar mechanism for regulating nicotinic acid degradation.

Quantifying outcome misclassification in multi-database studies: The case study of pertussis in the ADVANCE project

BACKGROUND

The Accelerated Development of VAccine beNefit-risk Collaboration in Europe (ADVANCE) is a public-private collaboration aiming to develop and test a system for rapid benefit-risk (B/R) monitoring of vaccines using European healthcare databases. Event misclassification can result in biased estimates. Using different algorithms for identifying cases of Bordetella pertussis (BorPer) infection as a test case, we aimed to describe a strategy to quantify event misclassification, when manual chart review is not feasible.

METHODS

Four participating databases retrieved data from primary care (PC) setting: BIFAP: (Spain), THIN and RCGP RSC (UK) and PEDIANET (Italy); SIDIAP (Spain) retrieved data from both PC and hospital settings. BorPer algorithms were defined by healthcare setting, data domain (diagnoses, drugs, or laboratory tests) and concept sets (specific or unspecified pertussis). Algorithm- and database-specific BorPer incidence rates (IRs) were estimated in children aged 0-14 years enrolled in 2012 and 2014 and followed up until the end of each calendar year and compared with IRs of confirmed pertussis from the ECDC surveillance system (TESSy). Novel formulas were used to approximate validity indices, based on a small set of assumptions. They were applied to approximately estimate positive predictive value (PPV) and sensitivity in SIDIAP.

RESULTS

The number of cases and the estimated BorPer IRs per 100,000 person-years in PC, using data representing 3,173,268 person-years, were 0 (IR = 0.0), 21 (IR = 4.3), 21 (IR = 5.1), 79 (IR = 5.7), and 2 (IR = 2.3) in BIFAP, SIDIAP, THIN, RCGP RSC and PEDIANET respectively. The IRs for combined specific/unspecified pertussis were higher than TESSy, suggesting that some false positives had been included. In SIDIAP the estimated IR was 45.0 when discharge diagnoses were included. The sensitivity and PPV of combined PC specific and unspecific diagnoses for BorPer cases in SIDIAP were approximately 85% and 72%, respectively.

CONCLUSION

Retrieving BorPer cases using only specific concepts has low sensitivity in PC databases, while including cases retrieved by unspecified concepts introduces false positives, which were approximately estimated to be 28% in one database. The share of cases that cannot be retrieved from a PC database because they are only seen in hospital was approximately estimated to be 15% in one database. This study demonstrated that quantifying the impact of different event-finding algorithms across databases and benchmarking with disease surveillance data can provide approximate estimates of algorithm validity.

Pertussis over two decades: seroepidemiological study in a large population of the Siena Province, Tuscany Region, Central Italy

OBJECTIVES

To evaluate seroprevalence against Bordetella pertussis in Tuscany, a large Italian region, from 1992 to 2005 and from 2013 to 2016.

DESIGN

Seroepidemiological study.

PARTICIPANTS

1812 serum samples collected in Tuscany from subjects older than 12 years from 1992 to 2005 and from 2013 to 2016.

OUTCOME MEASURES

Specific antibody levels were determined by means of standard commercial ELISA using a dual cut-off of 50 and 125 IU/mL as markers of past and recent infection/vaccination, respectively.

RESULTS

The highest values of IgG titres were observed in 1992-1994 in all subjects (69.5 IU/mL), with prevalence values of subjects with IgG titres of >50 and >125 IU/mL of 68.3% and 23.8%, respectively. IgG titres decreased in the years thereafter (37.8 IU/mL in 2002-2005), together with prevalence values (41.7% and 8.1% in 2002-2005). In 2013-2016, both IgG titres and prevalence values showed a slight increase (50.6 IU/mL, 53.9% and 14.7%, respectively). IgG titres and prevalence followed the same age-related trend in all time periods considered, with the highest values in subjects aged 12-22 years. The lowest values were found in the age group of subjects aged 23-35 years (OR 0.54).

CONCLUSIONS

Since 2002, approximately half of the population over 22 years of age have low IgG titres and are presumably susceptible to acquiring and transmitting pertussis infection. In addition, in 2013-2016, almost one-third of subjects aged 12-22 years, that is, the age group most likely to have been vaccinated against pertussis in infancy, had low antibody levels. Improving vaccination coverage and implementing careful surveillance are therefore recommended in order to prevent morbidity and mortality due to pertussis.

Pertussis hospitalizations among term and preterm infants: clinical course and vaccine effectiveness

BACKGROUND

Pertussis causes severe disease in young unvaccinated infants, with preterms potentially at highest risk. We studied pertussis in hospitalized infants as related to gestational age (GA) and vaccination history.

METHODS

Medical record data of 0-2y old patients hospitalized for pertussis during 2005-2014 were linked to vaccination data. Multivariable logistic regression was used to study the association between GA and vaccination history on the clinical disease course. We compared vaccine effectiveness (VE) against hospitalization for pertussis between term and preterm infants (i.e., <37w GA) using the screening method as developed by Farrington.

RESULTS

Of 1187 records, medical data from 676 were retrieved. Of these, 12% concerned preterms, whereas they are 8% of Dutch birth cohorts. Median age at admission was 3 m for preterms and 2 m for terms (p < 0.001). Preterms more often had received pertussis vaccination (62% vs 44%; p = 0.01) and more often had coinfections (37% vs 21%; p = 0.01). Preterms tended more often to have complications, to require artificial respiration or to need admittance to the intensive care unit (ICU). Preterms had longer ICU stays (15d vs 9d; p = 0.004). Vaccinated preterms and terms had a lower median length of hospital stay and lower crude risks of apneas and the need for artificial respiration, additional oxygen, and ICU admittance than those not vaccinated. After adjustment for presence of coinfections and age at admittance, these differences were not significant, except the lower need of oxygen treatment in vaccinated terms. Effectiveness of the first vaccination against pertussis hospitalizations was 95% (95% CI 93-96%) and 73% (95% CI 20-91%) in terms and preterms, respectively. Effectiveness of the second dose of the primary vaccination series was comparable in both groups (86 and 99%, respectively).

CONCLUSIONS

Infants hospitalized for pertussis suffer from severe disease. Preterms were overrepresented, with higher need for intensive treatment and less VE of first vaccination. These findings stress the need for alternative prevention, in particular prenatal vaccination of mothers, to reduce pertussis in both groups.

Timeliness of immunisations in preterm infants in the Netherlands

BACKGROUND

In the Netherlands, preterm infants receive the immunisations at the same chronological age as recommended for term infants without correction for gestational age (GA). The aim of this paper was to describe the timeliness of the routine Dutch national immunisation schedule in preterm infants in their first year of life and to evaluate possible determinants of delay.

METHODS

Preterm infants were prospectively recruited between October 2015 and October 2017 and stratified according to GA (<28, 28-32 and 32-36 weeks). Data from the baseline parental questionnaire, monthly parental questionnaires and medical records were used to determine the immunisation age and proportion of infants timely receiving the first immunisations (between 42 and 63 days). Results were compared between the GA and birth weight (BW) groups. Determinants associated with timeliness of immunisation were studied by multivariate logistic regression analysis.

RESULTS

Timely start of immunisation occurs in 60.5% of preterm infants in the Netherlands. The proportion of infants receiving the first immunisation on time was lowest for the group with GA <28 weeks (37%). The mean age of the first immunisation across all GA groups was 62.7 days (range 33-118) and differed significantly between GA group <28 weeks and the other two GA groups of 28-32 and 32-36 weeks (p < 0.001). Similar results were seen when stratified by BW. Multivariate analysis showed that low socioeconomic status (SES) and prolonged hospitalisation beyond 37 weeks each negatively influenced timeliness of the first immunisation.

CONCLUSION

These findings indicate that start of immunisations was often delayed in prematures and differs for different GA groups, being lowest (37%) in infants <28 weeks GA. Lower SES and prolonged hospital stay beyond 37 weeks GA are important determinants of timeliness. Efforts to improve timeliness should focus most on counselling parents in lower SES.

Pertussis diagnostic practices of general practitioners in the Netherlands: A survey study

Background: Pertussis testing is most important when transmission to vulnerable groups is likely. Patients with signs and symptoms suggestive of pertussis are prevalent in primary care, yet general practitioners' (GPs) reasons (not) to test for pertussis are largely unknown.Objectives: To evaluate GP-reported diagnostic practices for pertussis, reasons for (not) testing and intentions towards testing among GPs.Methods: A total of 594 Dutch GPs were invited by email to participate in a survey study including a questionnaire reflecting on their pertussis diagnostic practices, reasons for (not) testing and the intention to test for pertussis in the year of 2013. Intention to test was measured as the likelihood to test for eight clinical vignettes.Results: In total, 122 GPs (21%) completed the online questionnaire. Most GPs reported having diagnosed at least one pertussis case (84%) in the previous year. Of all GPs, 14% did not perform any pertussis tests in the last year. The most reported reason for testing was to confirm the clinical pertussis diagnosis (70%); the most reported reason for not testing was that the diagnostic test result does not influence treatment (70%). Overall, judging from the clinical vignettes, GPs reported being more likely to perform diagnostic testing based on symptoms than based on vulnerable groups at risk.Conclusion: In contrast to national guidelines, our results suggest that GPs report to test for pertussis mainly based on clinical symptoms rather than based on protecting vulnerable groups at risk.

Assays for Determining Pertussis Toxin Activity in Acellular Pertussis Vaccines

Whooping cough is caused by the bacterium Bordetella pertussis. There are currently two types of vaccines that can prevent the disease; whole cell vaccines (WCV) and acellular vaccines (ACV). The main virulence factor produced by the organism is pertussis toxin (PTx). This toxin is responsible for many physiological effects on the host, but it is also immunogenic and in its detoxified form is the main component of all ACVs. In producing toxoid for vaccines, it is vital to achieve a balance between sufficiently detoxifying PTx to render it safe while maintaining enough molecular structure that it retains its protective immunogenicity. To ensure that the first part of this balancing act has been successfully achieved, assays are required to accurately measure residual PTx activity in ACV products accurately. Quality control assays are also required to ensure that the detoxification procedures are robust and stable. This manuscript reviews the methods that have been used to achieve this aim, or may have the potential to replace them, and highlights their continuing requirement as vaccines that induce a longer lasting immunity are developed to prevent the re-occurrence of outbreaks that have been observed recently.

The burden of pertussis in older adults: what is the role of vaccination? A systematic literature review

INTRODUCTION

Pertussis (whooping cough) is a vaccine-preventable disease; however, neither natural- nor vaccine-induced protection is life-long. Although generally not severe in adults, pertussis can be associated with complications in patients with chronic conditions such as asthma or chronic obstructive pulmonary disease, and can be readily transmitted to more vulnerable populations, including neonates before they complete their primary vaccination. Furthermore, as the global population ages, the health and economic burden of the disease is expected to rise. Areas covered: A systematic literature review was conducted to ascertain the current epidemiological and financial burden of pertussis in older adults and to discuss the potential value of a booster vaccination in this population. Expert commentary: Our review indicates a considerable underestimation of the pertussis burden amongst older adults. Seroprevalence studies consistently demonstrate that the reported incidence may be much lower than the actual incidence. Tetanus toxoid-reduced diphtheria toxoid and acellular pertussis vaccines are immunogenic in older adults, induce high booster responses and are well-tolerated. There is therefore a good rationale for the advocacy of booster pertussis vaccination throughout life to prevent pertussis infection and its transmission, especially in adults aged ≥50 years.

Does the economic recession influence the incidence of pertussis in a cosmopolitan European city?

Background

In the last few years, pertussis has re-emerged worldwide. The aim of this article is to study how the incidence of the disease has evolved in Barcelona city over a 16-year period, and determine which factors are associated with the evolution of the disease. We discuss the causes of the observed changes considering different possibilities such as vaccination coverage, vaccine effectiveness, increased surveillance or the effect of the current economic recession.

Methods

We performed a cross-sectional, observational, population-based descriptive study using data for the 2000–2015 period from the notifiable diseases register maintained by Barcelona Public Health Agency. We used Poisson regression to compute adjusted odds ratios (aOR) and their corresponding 95% confidence intervals (CI).

Results

A total of 1791 cases were registered. The incidence of the disease increased throughout the city from 2011 onwards. While children under 1 year of age had the highest-incidence and were the most at risk (aOR = 27.18, CI:23.51–31.44), we found that the age of affected children was higher in the last years. Incidence proportion (PRR) was lower among foreign-born children than native children (PRR = 0.43 CI:0.32–0.58). In the whole-cell vaccine period (2000–2004), the percentage of cases under 1 year of age who received the vaccine was lower than in 2005–2015 when the acellular vaccine was used (p = 0.01), suggesting a lower efficacy of the acellular vaccine. However, vaccination coverage in children under 6 years remained high (~ 90%), and there were no significant year-to-year variations (p = 0.757). Moreover, there did not appear to be any significant restrictions in medical care. According to the index of disposable household income (DHI), pertussis incidence increased from 2011 onwards in all neighbourhoods and remained higher in those with lower DHI.

Conclusions

The noteworthy increase in pertussis incidence does not seem to be due to the economic recession, but to other factors here described.

The Role of Mucosal Immunity in Pertussis

Pertussis or whooping cough, mainly caused by Bordetella pertussis, is a severe respiratory disease that can affect all age groups but is most severe and can be life-threatening in young children. Vaccines against this disease are widely available since the 1950s. Despite high global vaccination coverage, the disease is not under control in any country, and its incidence is even increasing in several parts of the world. Epidemiological and experimental evidence has shown that the vaccines fail to prevent B. pertussis infection and transmission, although they are very effective in preventing disease. Given the high infection rate of B. pertussis, effective control of the disease likely requires prevention of infection and transmission in addition to protection against disease. With rare exceptions B. pertussis infections are restricted to the airways and do not usually disseminate beyond the respiratory epithelium. Therefore, protection at the level of the respiratory mucosa may be helpful for an improved control of pertussis. Yet, compared to systemic responses, mucosal immune responses have attracted relatively little attention in the context of pertussis vaccine development. In this review we summarize the available literature on the role of mucosal immunity in the prevention of B. pertussis infection. In contrast to vaccination, natural infection in humans and experimental infections in animals induce strong secretory IgA responses in the naso-pharynx and in the lungs. Several studies have shown that secretory IgA may be instrumental in the control of B. pertussis infection. Furthermore, studies in mouse models have revealed that B. pertussis infection, but not immunization with current acellular pertussis vaccines induces resident memory T cells, which may also contribute to protection against colonization by B. pertussis. As these resident memory T cells are long lived, vaccines that are able to induce them should provide long-lasting immunity. As of today, only one vaccine designed to induce potent mucosal immunity is in clinical development. This vaccine is a live attenuated B. pertussis strain delivered nasally in order to mimic the natural route of infection. Due to its ability to induce mucosal immunity it is expected that this approach will contribute to improved control of pertussis.

PERISCOPE: road towards effective control of pertussis

The resurgence and changing epidemiology of pertussis in high-income countries, the high infant mortality caused by pertussis in low-income countries, and the increasing morbidity in all age groups worldwide call for a concerted effort to both improve the current vaccines and develop new vaccines and vaccination strategies against pertussis. In this Personal View, we identify several key obstacles on the path to developing a durable solution for global control of pertussis. To systematically address these obstacles, the PERtussIS Correlates Of Protection Europe (PERISCOPE) Consortium was established in March, 2016. The objectives of this consortium are to increase scientific understanding of immunity to pertussis in humans induced by vaccines and infections, to identify biomarkers of protective immunity, and to generate technologies and infrastructure for the future development of improved pertussis vaccines. By working towards the accelerated licensure and implementation of novel, well tolerated, and effective pertussis vaccines, we hope to strengthen and stimulate further collaboration and transparency between the key stakeholders, including the public, the scientific community, public health institutes, regulatory authorities, and vaccine manufacturers.

IL-17-dependent SIgA-mediated protection against nasal Bordetella pertussis infection by live attenuated BPZE1 vaccine

BPZE1 is a live attenuated Bordetella pertussis vaccine for nasal administration to mimic the natural route of infection. Here, we studied the mechanism of BPZE1-induced immunity in the murine nasal cavity in contrast to acellular vaccine (aPV), although both vaccines protected against lung colonization. Transfer of splenocytes or serum from BPZE1-vaccinated or aPV-vaccinated mice protected naïve mice against lung colonization but not against nasal colonization. However, transfer of nasal washes from BPZE1-vaccinated mice resulted in protection against nasal colonization, which was lost in IgA-deficient or poly-Ig receptor-deficient mice, indicating that it depends on secretory IgA (SIgA) induction induced in the nose. BPZE1-induced protection against nasal colonization was long-lived despite the relatively rapid decay of SIgA, indicating a potent BPZE1-induced local memory response, likely due to CD4⁺ tissue-resident memory T cells induced in the nose by BPZE1. These cells produced interleukin-17 (IL-17), known to be important for SIgA secretion. Furthermore, BPZE1 failed to protect Il17^-/- mice against nasal colonization by B. pertussis and induced only background levels of nasal SIgA. Thus, our results show important differences in the protective mechanism between the upper and the lower murine respiratory tract and demonstrate an IL-17-dependent SIgA-mediated mechanism of BPZE1-induced protection against B. pertussis nasopharyngeal colonization.

The pertussis hypothesis: Bordetella pertussis colonization in the etiology of asthma and diseases of allergic sensitization

Decades of peer reviewed evidence demonstrate that: 1)Bordetellapertussisand pertussis toxin are potent adjuvants, inducing asthma and allergic sensitization in animal models of human disease, 2)Bordetella pertussisoften colonizes the human nasopharynx, and is well documented in highly pertussis-vaccinated populations and 3) in children, a history of whooping cough increases the risk of asthma and allergic sensitization disease. We build on these observations with six case studies and offer a pertussis-based explanation for the rapid rise in allergic disease in former East Germany following the fall of the Berlin Wall; the current asthma, peanut allergy, and anaphylaxis epidemics in the United States; the correlation between the risk of asthma and gross national income per capita by country; the lower risk of asthma and allergy in children raised on farms; and the reduced risk of atopy with increased family size and later sibling birth order. To organize the evidence for the pertussis hypothesis, we apply the Bradford Hill criteria to the association between Bordetella pertussisand asthma and allergicsensitization disease. We propose that, contrary to conventional wisdom that nasopharyngealBordetella pertussiscolonizing infections are harmless, subclinicalBordetella pertussiscolonization is an important cause of asthma and diseases of allergic sensitization.

Pertussis surveillance by small serosurveys of blood donors

Serosurveys have established data about the distribution of immunoglobulin G (IgG)-antibodies to pertussis toxin (PT) in various populations. We tried to detect whether small serosurveys in blood donors could serve as a simple and inexpensive means to collect information about the circulation of Bordetella pertussis. We screened every donation in 307 adult blood donors aged 19-69 years for IgG-anti-PT by standardised enzyme-linked immunosorbent assays (ELISA), and the donors were followed between 2014 and 2016 for a total of 426 person-years. When we used a vertical survey with cut-offs of 100, 62.5 and 40 IU/ml, respectively, as an indicator for recent contacts with B. pertussis, nine (2.9%), 22 (7.2%) and 54 (17.6%) of donors had IgG-anti-PT titres above the respective levels. During the horizontal observation period of 426 person years, six significant increases and two conversions were found, which lead to an estimate of 1878 contacts/100.000 person-years (1.9% per year). Median and mean IgG-anti-PT concentrations remained relatively stable from year to year during the observation period. Our findings show that small serosurveys of blood donors offer a simple and cheap method for the surveillance of B. pertussis.

Prospective multinational serosurveillance study of Bordetella pertussis infection among 10- to 18-year-old Asian children and adolescents

OBJECTIVES

Bordetella pertussis continues to cause outbreaks worldwide. To assess the role of children and adolescent in transmission of pertussis in Asia, we performed a multinational serosurveillance study.

METHODS

From July 2013 to June 2016, individuals aged 10 to 18 years who had not received any pertussis-containing vaccine within the prior year were recruited in 10 centres in Asia. Serum anti-pertussis toxin (PT) IgG was measured by ELISA. Demographic data and medical histories were obtained. In the absence of pertussis immunization, anti-PT IgG ≥62.5 IU/mL was interpreted as B. pertussis infection within 12 months prior, among them levels ≥125 IU/mL were further identified as infection within 6 months.

RESULTS

A total of 1802 individuals were enrolled. Anti-PT IgG geometric mean concentration was 4.5, and 87 (4.8%) individuals had levels ≥62.5 IU/mL; among them, 73 (83.9%) had received three or more doses of pertussis vaccine before age 6 years. Of 30 participants with persistent cough during the past 6 months, one (3.3%) had level ≥125 IU/mL. There was no significant difference in proportions with anti-PT IgG ≥62.5 IU/mL among age groups (13-15 vs. 10-12 years, 16-18 vs. 10-12 years), between types of diphtheria, pertussis and tetanus (DTP; whole cell vs. acellular), number of doses before age 6 years within the DTP whole-cell pertussis vaccine (five vs. four doses) or acellular pertussis vaccine (five vs. four doses) and history of persistent cough during the past 6 months (yes vs. no).

CONCLUSIONS

There is significant circulation of B. pertussis amongst Asian children and adolescents, with one in 20 having serologic evidence of recent infection regardless of vaccination background.

Enhanced Bordetella pertussis acquisition rate in adolescents during the 2012 epidemic in the Netherlands and evidence for prolonged antibody persistence after infection

In 2012 a large epidemic of pertussis occurred in the Netherlands. We assessed pertussis toxin (PT) antibody levels in longitudinal serum samples from Dutch 10–18 year-olds, encompassing the epidemic, to investigate pertussis infection incidence. Methods: Blood was sampled in October 2011 (n = 239 adolescents), then 1 year (2012; n = 228) and 3 years (2014; n = 167) later. PT-IgG concentrations were measured by immunoassay and concentrations ≥50 IU/mL (seropositive) assumed indicative of an infection within the preceding year. Results: During the 2012 epidemic, 10% of participants became seropositive, while this was just 3% after the epidemic. The pertussis acquisition rate proved to be sixfold higher during the epidemic (97 per 1,000 person-years) compared with 2012–2014 (16 per 1,000 person-years). In 2012, pertussis notifications among adolescents nationwide were 228/100,000 (0.23%), which is at least 40 times lower than the seropositivity percentage. Remarkably, 17 of the 22 seropositive participants in 2011, were still seropositive in 2012 and nine remained seropositive for at least 3 years. Discussion: Longitudinal studies allow a better estimation of pertussis infections in the population. A PT-IgG concentration ≥50 IU/mL as indication of recent infection may overestimate these numbers in cross-sectional serosurveillance and should be used carefully.

Robust Humoral and Cellular Immune Responses to Pertussis in Adults After a First Acellular Booster Vaccination

Introduction

To reduce the pertussis disease burden, nowadays several countries recommend acellular pertussis (aP) booster vaccinations for adults. We aimed to evaluate the immunogenicity of a first adult aP booster vaccination at childbearing age.

Methods

In 2014, healthy adults aged 25–29 years (n = 105), vaccinated during infancy with four doses of whole-cell pertussis (wP) vaccine, received a Tdap (tetanus, diphtheria, and aP) booster vaccination. Blood samples were collected longitudinally pre-booster, 2 and 4 weeks, and 1 year and 2 years post-booster. Tdap vaccine antigen-specific antibody levels and memory B- and T-cell responses were determined at all time points. Antibody persistence was calculated using a bi-exponential decay model.

Results

Upon booster vaccination, the IgG levels specific to all Tdap vaccine antigens were significantly increased. After an initial rapid decline in the first year, PT-IgG antibody decay was limited (15%) in the second year post-booster. The duration of a median level of PT-IgG ≥20 IU/mL was estimated to be approximately 9 years. Vaccine antigen-specific memory B- and T-cell numbers increased and remained at high levels although a significant decline was observed after 4 weeks post-booster. However, Th1, Th2, and Th17 cytokine production remained above pre-booster levels for 2 years.

Conclusion

The Tdap booster vaccination in wP-primed Dutch adults induced robust long-term humoral and cellular immune responses to pertussis antigens. Furthermore, PT-IgG levels are predicted to remain above the presumed protective cut-off for at least 9 years which might deserves further attention in evaluating the current recommendation to revaccinate women during every new pregnancy.

Pertussis surveillance and control: exploring variations and delays in testing, laboratory diagnostics and public health service notifications, the Netherlands, 2010 to 2013

Pertussis is most severe among unvaccinated infants (< 1 year of age), and still leads to several reported deaths in the Netherlands every year. In order to avoid pertussis-related infant morbidity and mortality, pertussis surveillance data are used to guide pertussis control measures. However, more insight into the accuracy of pertussis surveillance and control, and into the range of healthcare and public health-related factors that impede this are needed. We analysed a unique combination of data sources from one Dutch region of 1.1 million residents, including data from laboratory databases and local public health notifications between 2010 and 2013. This large study (n = 12,090 pertussis tests) reveals possible misdiagnoses, substantial under-notification (18%, 412/2,301 laboratory positive episodes) and a delay between patient symptoms and notification to the local public health services (median 34 days, interquartile range (IQR): 27–54). It is likely that the misdiagnoses, under-notification and overall delay in surveillance data are not unique to this area of the Netherlands, and are generalisable to other countries in Europe. In addition to preventive measures such as maternal immunisation, based on current findings, we further recommend greater adherence to testing guidelines, standardisation of test interpretation guidelines, use of automatic notification systems and earlier preventive measures.

Temporally Varying Relative Risks for Infectious Diseases: Implications for Infectious Disease Control

Risks for disease in some population groups relative to others (relative risks) are usually considered to be consistent over time, although they are often modified by other, nontemporal factors. For infectious diseases, in which overall incidence often varies substantially over time, the patterns of temporal changes in relative risks can inform our understanding of basic epidemiologic questions. For example, recent studies suggest that temporal changes in relative risks of infection over the course of an epidemic cycle can both be used to identify population groups that drive infectious disease outbreaks, and help elucidate differences in the effect of vaccination against infection (that is relevant to transmission control) compared with its effect against disease episodes (that reflects individual protection). Patterns of change in the age groups affected over the course of seasonal outbreaks can provide clues to the types of pathogens that could be responsible for diseases for which an infectious cause is suspected. Changing apparent efficacy of vaccines during trials may provide clues to the vaccine's mode of action and/or indicate risk heterogeneity in the trial population. Declining importance of unusual behavioral risk factors may be a signal of increased local transmission of an infection. We review these developments and the related public health implications.

Seroepidemiology of diphtheria and pertussis in Chongqing, China: serology-based evidence of Bordetella pertussis infection

OBJECTIVES

In order to gain further insight into the seroepidemiology of Bordetella pertussis infection and immunity against diphtheria in Chongqing, China, the concentrations of antibodies to pertussis toxin (PT) and diphtheria toxin (DT) were investigated in a healthy population.

STUDY DESIGN

Cross-sectional study.

METHODS

In total, 1080 healthy people were recruited into this study. Sera antibodies to DT and PT were measured quantitatively using commercial enzyme-linked immunosorbent assay kits. Age-specific incidence of infection with B. pertussis was estimated and compared with notified cases of pertussis.

RESULTS

The mean concentration of anti-DT IgG was 0.71 IU/ml (95% confidence interval [CI] = 0.60-0.82), with a positive rate (>0.01 IU/ml) of 97.41% (1052/1080). The mean concentration of anti-PT IgG was 7.65 IU/ml (95% CI = 6.65-8.65), with a positive rate (>100 IU/ml) of 1.17% (11/944). The estimated pertussis infection rate was 7290/100,000, which was far higher than the reported incidence of 1.29/100,000 in 2015. The peaks of estimated incidence of infection were found in subjects aged 7-14 years (9971/100,000) and ≥20 years (13,898/100,000).

CONCLUSIONS

B. pertussis infection occurs frequently in young infants and adolescents/adults; the latter are often responsible for the transmission of pertussis to young infants. The existing surveillance system may underestimate the true incidence of pertussis in older age groups in Chongqing, and the immunisation programme should be improved to provide protection against pertussis for adolescents and young adults.

Whither vaccines?

Currently used vaccines have had major effects on eliminating common infections, largely by duplicating the immune responses induced by natural infections. Now vaccinology faces more complex problems, such as waning antibody, immunosenescence, evasion of immunity by the pathogen, deviation of immunity by the microbiome, induction of inhibitory responses, and complexity of the antigens required for protection. Fortunately, vaccine development is now incorporating knowledge from immunology, structural biology, systems biology and synthetic chemistry to meet these challenges. In addition, international organisations are developing new funding and licensing pathways for vaccines aimed at pathogens with epidemic potential that emerge from tropical areas.