[Two children in the Netherlands with a Corynebacterium diphtheriaeinfection]. / Twee kinderen in Nederland met eenCorynebacterium diphtheriae-infectie.

Infections with Corynebacterium diphtheriae were virtually absent among the Dutch population due to vaccination, while in the first half of the 20th century, it was a significant cause of child mortality. However, due to imported infections resulting from migration from countries with low vaccination coverage, infections with Corynebacterium diphtheriae are resurging. Concurrently, the vaccination rates among Dutch children are decreasing, elevating the risk of outbreaks. Severe symptoms are caused by exotoxins from the C. diphtheriae, infections with non-toxigenic strains can occur, which vaccination does not protect against. The bacteria itself is rarely invasive; only the toxin spreads. Non-toxin-producing strains manifest locally with milder symptoms but can become invasive, causing bacteraemia and endocarditis. As infections with non-toxigenic strains are not notifiable, little is known about their epidemiology. Moreover, specific culture media are required for bacterial cultivation, potentially leading to missed diagnoses.

A prospective, observational, multi-center, post-marketing safety surveillance study of the GSK combined vaccine against diphtheria, tetanus, pertussis, poliomyelitis, and Haemophilus influenzae type b invasive infections (DTaP-IPV/Hib) in South Korean infants.

In South Korea, a combined vaccine against diphtheria, tetanus, pertussis, poliomyelitis, and Haemophilus influenzae type b invasive infections (DTaP-IPV/Hib) is available since 2018 for vaccination of infants from the age of 2 months. This prospective, observational, non-comparative, post-marketing study evaluated the real-world safety of DTaP-IPV/Hib primary vaccination in eligible South Korean infants from the age of 2 months between 2018 and 2022. Infants were followed up for 30 days after each vaccine dose to assess the proportion of infants experiencing any adverse event (AE), including adverse drug reactions (ADRs), unexpected AEs, and serious AEs/serious ADRs (SAEs/SADRs). Of 660 infants vaccinated during the study period, 646 were included in the total safety cohort. A total of 194 AEs were reported in 143 (22.1%) infants; 158 AEs occurred after the first dose in 130 (20.1%) infants, 21 after the second dose in 20 (13.4%) infants, and 11 after the third dose in ten (8.1%) infants. The most frequent AEs by Medical Dictionary for Regulatory Activities Preferred Terms terminology were pyrexia (13.3%), injection site swelling (5.1%), and irritability (1.7%). Most of the AEs were mild, resolved without a medical visit, and were classified as possibly related to vaccination. The incidence proportions of ADRs, unexpected AEs, and SAEs/SADRs were 19.4%, 4.3%, and 0.9%, respectively. All SAEs/SADRs resolved after hospitalization or emergency room visit, and one event was possibly related to vaccination. These results are in line with the approved label and other national/international studies, confirming the acceptable safety profile of DTaP-IPV/Hib in the South Korean pediatric population.

In South Korea, a vaccine to help protect infants against five childhood diseases (diphtheria, tetanus, whooping cough, poliomyelitis, and Haemophilus influenzae type b invasive infections) called DTaP-IPV/Hib vaccine, has been available since 2018. As required by Korean regulation, this study aimed to confirm that DTaP-IPV/Hib was well tolerated by South Korean infants during its first 4 years of use in the country (2018­2022). This study followed 646 healthy infants aged 2­3 months who received up to three vaccine doses with 2-month intervals between doses, according to the Korean vaccination recommendations. The infants were followed for 30 days after each vaccination to evaluate how often adverse events (AEs) occurred during that period. An AE was defined as any untoward medical event after exposure to the vaccine, but not necessarily caused by that same vaccine. Overall, 194 AEs occurred during the study. On average, at least one AE was reported in 22% of infants within 30 days following vaccination. These AEs were mostly fever (body temperature >38.0°C), swelling at vaccine injection site, and irritability. A serious AE (SAE) was reported for 0.9% of infants. The infants always recovered from these SAEs after hospitalization or emergency room visit. The reported AEs are indicated in the vaccine package insert, meaning they were possibly expected to occur after vaccination. This study therefore confirms the acceptable safety profile of DTaP-IPV/Hib when given to South Korean infants in accordance with local prescribing recommendations and as part of routine childhood immunization.

Risk factors of diphtheria outbreak in damt district of Al Dhalea Governorate, 2023 -Yemen: a case-control study.

BACKGROUND: In Yemen, diphtheria has become an important health problem since 2017 when diphtheria re-emergence as a consequence of war and the collapse of the health system. In 2023, there has been a 57% increase in diphtheria cases compared to 2021 and 2022. Damt district of Al Dhalea Governorate had the highest reported cases for year 2023. The study aims to determine the risk factors associated with diphtheria outbreak in Damt District. METHODS: A retrospective matched case-control (1:2) was used. All confirmed cases based on the WHO case definition reported from Damt district during 2023 were considered cases. Two age-matched (± 5years) neighborhood controls were recruited per case. A pretested questionnaire was used for collecting data during household interviews including demographic and household characteristics, knowledge of diphtheria, vaccination status, contact with a case of diphtheria, and travel history. Frequency and proportion for quantitative and median with interquartile range (IQR) for quantitative variables. Chi-square and Mann-Whitney tests to compare the distribution of categorical and numerical variables between cases and controls. Univariate and multivariate conditional binary logistic regression, and Adjusted Odds ratio (AOR) with a 95% confidence interval at P < 0.05 were used to identify risk factors. RESULTS: A total of 118 cases and 236 controls were enrolled, 56% were females (63% of cases vs. 53% of controls). The median (IQR) age was 14 (9,22) years for cases vs 12(7,23) of control, it was significantly higher for females than males in the case group: (16(10,29) Vs 10(6,18), P < 0.001) and control group: (15(8,25) vs 12(7,18), p-value = 0.022). Partial vaccination status AOR = 13.7(6.1-31.1), P-value < 0.001), contacts with a case of diphtheria AOR = 8.5(2.3-31.0), P value < 0.001) and Female gender, AOR = 3.3(CI; 1.1-9.5, P value = 0.029), were the main risk factors. CONCLUSIONS: Poor vaccination and contact with a case of diphtheria were the main contributors to diphtheria in the Damt district particularly among adult females. Increasing the vaccination coverage with a diphtheria-containing vaccine through routine immunization as well as tetanus-diphtheria vaccine for childbearing age females along with community awareness regarding protection measures during home care of diphtheria cases. Vaccination services as well as gender barriers related to Td vaccination should be investigated.

Seroprevalence of anti-diphtheria toxoid antibody and implications for vaccination policy in Vietnam's South-central coast: a cross-sectional study.

BACKGROUND: Diphtheria is a re-emerging infectious disease and public health concern worldwide and in Vietnam with increasing cases in recent years. This study aimed to assess the anti-diphtheria toxoid antibodies status in Khanh Hoa Province and identify factors contributing to the vaccination policy in the south-central coast of Vietnam. METHODS: This was a cross-sectional study to evaluate the seroprevalence of anti-diphtheria toxoid antibodies among 1,195 participants, aged 5 - 40 years in Khanh Hoa Province, Vietnam. Immunoglobulin G antibody levels against diphtheria were detected using a commercial anti-diphtheria toxoid enzyme-linked immunosorbent assay (SERION ELISA classic Diphtheria Immunoglobulin G) and were categorized following the World Health Organization guidelines. RESULTS: The mean anti-diphtheria toxoid antibody levels were 0.07 IU/ml (95% Confidence Interval: 0.07-0.08). Anti-diphtheria toxoid antibody levels were found to be associated with age and history of diphtheria vaccination. The 5-15 years age group had the highest levels (0.09 IU/ml), while the older age group had the lowest antibody level (p < 0.001). Individuals who received three doses (adjusted Odds ratio: 2.34, 95%CI: 1.35 - 4.07) or 4+ doses (adjusted Odds ratio: 2.45, 95%CI: 1.29 - 4.64) had a higher antibody level compared to those who received only one dose regardless of age. CONCLUSION: It is crucial to promote routine vaccination coverage to over 95% for children under one year of age with three primary doses of the diphtheria-containing vaccine, including additional doses at 18 months and 7 years of age. Booster doses should be promoted and administered to adolescents and adults every 10 years.

Respiratory diphtheria in the time of Omicron.

Abstract: Diphtheria is a potentially fatal bacterial infection caused by toxin-producing strains of corynebacteria, most often Corynebacterium diphtheriae and less commonly Corynebacterium ulcerans. Incidence of the disease has fallen significantly since the introduction of vaccination programs; it is now rare in countries with high vaccination coverage such as Australia. This article presents the most recent respiratory cases of diphtheria in two children in New South Wales-the first locally acquired childhood cases in Australia in 30 years-and discusses potential contributing factors. These encompass the lack of clinical awareness and the delays in laboratory diagnosis in regional laboratories. The cases also highlight the problem of vaccine hesitancy and the role that primary carers play in addressing these anxieties. While clinical management of the cases progressed well, factors in the public health responses were complicated by access to appropriate care and by delays in antibiotic sensitivity profiles. The public health response to these cases raises important considerations for clinicians and public health practitioners, including preparedness for rare and re-emerging diseases, the need for culturally safe environments and the importance of addressing vaccine hesitancy. Preparedness requires consideration of the capacity of regional health systems with fewer resources and of how public health departments can support response to multiple crises. Preparedness also relies on access to necessary diagnostic laboratory resources, on up-to-date guidelines, and on maintaining awareness among clinicians for these rare infections.

Antibody persistence to diphtheria toxoid, tetanus toxoid, Bordetella pertussis antigens, and Haemophilus influenzae type b following primary and first booster with pentavalent versus hexavalent vaccines.

Thailand has incorporated the whole-cell (wP) pertussis vaccine into the expanded program on immunization since 1977 and has offered the acellular pertussis (aP) vaccine as an optional vaccine for infants since 2001. We followed healthy children from a clinical trial (ClinicalTrials.gov NCT02408926) in which children were randomly assigned to receive either pentavalent (DTwP-HB-Hib) or hexavalent (DTaP-IPV-HB-Hib) vaccines for their primary series (administered at 2, 4, and 6 months) and first booster vaccination (18 months). Both groups received Tdap-IPV as a second booster at the age of 4 y. Blood samples were collected for evaluation of antibody persistence to diphtheria toxoid (DT), tetanus toxoid (TT), and Bordetella pertussis (B. pertussis) between 2 and 6 y of age annually, and for the immunogenicity study of Tdap-IPV at 1 month after the second booster. Antibody persistence to Haemophilus influenzae type b (Hib) was followed until 3 y of age. A total of 105 hexavalent-vaccinated children and 91 pentavalent-vaccinated children completed this study. Both pentavalent and hexavalent groups demonstrated increased antibody levels against DT, TT, and B. pertussis antigens following the second booster with Tdap-IPV. All children achieved a seroprotective concentration for anti-DT and anti-TT IgG at 1 month post booster. The hexavalent group possessed significantly higher anti-pertactin IgG (adjusted p = .023), whereas the pentavalent group possessed significantly higher anti-pertussis toxin IgG (adjusted p < .001) after the second booster. Despite declining levels post-second booster, a greater number of children sustained protective levels of anti-DT and anti-TT IgG compared to those after the first booster.

Balto and Togo during the cold winter of Alaska (1925): the two canine heroes in the fight against diphtheria.

In recent years, diphtheria has re-emerged in areas with inadequate vaccination coverage, and Europe has not been spared with several cases among migrants. Diphtheria is a potentially fatal infection caused mainly by toxigenic strains of Corynebacterium diphtheriae. Due to the high mortality rate, especially among young children, the fight against diphtheria is considered one of the first conquests of immunization. In the history of medicine, there is a unique case of an unconventional response to a diphtheria outbreak in which sled dogs were used to overcome the supply difficulties of diphtheria antitoxin. The mass media followed the medical response to the outbreak and raised audience awareness of public health issues. The facts of Nome, Alaska, in 1925 can serve as a catalyst to rethink conventional responses to diphtheria outbreaks in low-income countries today and promote mass media awareness of public health importance.

Diphtheria in a Swiss Asylum Seeker Reception Centre: Outbreak Investigation and Evaluation of Testing and Vaccination Strategies.

Objectives: To describe a suspected diphtheria outbreak in a Swiss asylum seeker reception centre, and to analyse its management response regarding testing and vaccination. Methods: We retrospectively analysed clinical, microbiology, and case management data of all asylum seekers tested for C. diphtheriae between 28th August and 31st December 2022 while residing at the centre. Results are reported descriptively. Results: Among 265 individuals tested, ten cases of cutaneous diphtheria, one simultaneous respiratory and cutaneous case, and nine respiratory carriers were identified. Mass throat screening, targeted throat testing and targeted wound testing yielded 4.8%, 4.3%, and 17.4% positive results, respectively. No respiratory carrier was identified among cutaneous cases undergoing a throat swab, and no symptomatic case was identified among individuals with unspecific throat symptoms. Rates of vaccination implementation of newly arriving asylum seekers before and after the outbreak were low (17.5% and 15.5%, respectively), as were rates of targeted vaccination among cases and close contacts. Conclusion: We provide evidence for transmission both prior to arrival and within the setting, suboptimal practices and timeliness of testing, and implementation gaps in vaccination.

Immunogenicity and safety of adsorbed diphtheria-purified pertussis-tetanus-inactivated polio (Sabin strain)-Haemophilus type b conjugate combined vaccine (DPT-IPV-Hib) in healthy Japanese Infants ≥ 2 and < 43 months of Age: A phase III, multicenter, active controlled, assessor-blinded, randomized, parallel-group study.

OBJECTIVE: This study investigated the immunogenicity and safety of a pentavalent vaccine Gobik (DPT-IPV-Haemophilus influenzae type b [Hib]) in healthy Japanese infants aged ≥ 2 and < 43 months using a concomitant vaccination with ActHIB® (Hib) and Tetrabik (DPT-IPV) as a comparator. METHODS: This study was conducted as a phase 3, multicenter, active controlled, assessor-blinded, randomized, parallel-group study. Participants received a total of 4 subcutaneous doses (3 primary immunization doses and a booster dose) of either the experimental drug (DPT-IPV-Hib) or the active comparator (Hib + DPT-IPV). The primary endpoints were the anti-PRP antibody prevalence rate with ≥ 1 µg/mL, and the antibody prevalence rates against pertussis, diphtheria toxin, tetanus toxin, and attenuated poliovirus after the primary immunization. RESULTS: In 267 randomized participants (133 in the DPT-IPV-Hib group and 134 in the Hib + DPT-IPV group), the antibody prevalence rates after the primary immunization in both groups were 100.0 % and 88.7 % for anti-PRP antibody with ≥ 1 µg/mL, 99.2 % and 98.5 % against diphtheria toxin, and 100.0 % and 99.2 % against tetanus toxin, respectively. The antibody prevalence rates against pertussis and attenuated poliovirus were 100.0 % in both groups. The non-inferiority of the DPT-IPV-Hib group to the Hib + DPT-IPV group was verified for all measured antibodies. In both groups, all the GMTs of antibodies after the primary immunization were higher than those before the first dose, and those after the booster dose were higher than those after the primary immunization. No safety issues were identified. CONCLUSION: A single-agent Gobik, the first DPT-IPV-Hib pentavalent vaccine approved in Japan, was confirmed to simultaneously provide primary and booster immunizations against Hib infection, pertussis, diphtheria, tetanus, and poliomyelitis and to have a preventive effect and safety comparable to concomitant vaccination with Hib (ActHIB®) and DPT-IPV quadrivalent vaccine (Tetrabik).

Quantitative analysis of pertussis, tetanus, and diphtheria antibodies in sera and breast milk from Tdap vaccinated women using a qualified multiplex assay.

Pertussis (whooping cough) is a reemergent, highly contagious respiratory infection of public health concern. Infants prior to initiation of their primary vaccination series are the most vulnerable to severe infection, and even death. Vaccination during pregnancy is an efficacious means of reducing infection in infants. This approach relies on boosting maternal immunity and passive transfer of antibodies to the infant via placenta and breast milk. Similarly, maternal vaccination post-partum can enhance maternal-infant immunity. To support the analysis of pertussis immunity in the context of maternal-infant immunization, we developed a high throughput multiplex assay for simultaneous quantification of serum IgG antibodies against pertussis vaccine antigens: pertussis toxin (PT), filamentous hemagglutinin (FHA), pertactin (PRN), and fimbriae (FIM2/3), and against tetanus (TT) and diphtheria toxoids (DT), using the Meso Scale Discovery (MSD) platform. The assay was qualified, and specificity, sensitivity, accuracy, precision, linearity, and robustness were demonstrated. The assay was subsequently adapted for quantification of IgG and IgA in breast milk. Applied to a serological survey of pregnant women living in the United States and sub-Saharan Africa, this method revealed differences in magnitude and breadth of antibody profile, consistent with history of vaccination. A longitudinal analysis of Tdap responses in women vaccinated post-partum demonstrated a rapid increase in serum IgG that remained elevated for up to 24 months. Likewise, high levels of vaccine-specific IgA and IgG antibodies were present in breast milk, although they exhibited faster decay. This multiplex MSD assay is a reliable and practical tool for quantification of pertussis, tetanus, and diphtheria antibodies in serum and breast milk in serosurveys or vaccine studies. IMPORTANCE: Pertussis (whooping cough) has reemerged in recent years. Vaccination during pregnancy is an effective approach to prevent illness during the first months of life. We developed a multiplex assay for quantification of pertussis, tetanus, and diphtheria serum antibodies using the Meso Scale Discovery (MSD) platform; the method was qualified, and specificity, precision, accuracy, linearity, and limits of quantification were defined. It was also adapted for quantification of antibodies in breast milk. We successfully determined serostatus in women from different regions and with different vaccination histories, as well as responses to Tdap in blood and breast milk post-partum. This is the first description of a multiplex assay for the quantification of pertussis, tetanus, and diphtheria antibodies in breast milk.

Antiviral responses induced by Tdap-IPV vaccination are associated with persistent humoral immunity to Bordetella pertussis.

Many countries continue to experience pertussis epidemics despite widespread vaccination. Waning protection after booster vaccination has highlighted the need for a better understanding of the immunological factors that promote durable protection. Here we apply systems vaccinology to investigate antibody responses in adolescents in the Netherlands (N = 14; NL) and the United Kingdom (N = 12; UK) receiving a tetanus-diphtheria-acellular pertussis-inactivated poliovirus (Tdap-IPV) vaccine. We report that early antiviral and interferon gene expression signatures in blood correlate to persistence of pertussis-specific antibody responses. Single-cell analyses of the innate response identified monocytes and myeloid dendritic cells (MoDC) as principal responders that upregulate antiviral gene expression and type-I interferon cytokine production. With public data, we show that Tdap vaccination stimulates significantly lower antiviral/type-I interferon responses than Tdap-IPV, suggesting that IPV may promote antiviral gene expression. Subsequent in vitro stimulation experiments demonstrate TLR-dependent, IPV-specific activation of the pro-inflammatory p38 MAP kinase pathway in MoDCs. Together, our data provide insights into the molecular host response to pertussis booster vaccination and demonstrate that IPV enhances innate immune activity associated with persistent, pertussis-specific antibody responses.

Immunogenicity at delivery after Tdap vaccination in successive pregnancies.

Background: Tetanus, diphtheria, acellular pertussis (Tdap) vaccination is recommended to be administered in every pregnancy. Although the safety of this strategy has been confirmed, the immunogenicity of Tdap vaccination in two successive pregnancies has not yet been described. This study investigated Tdap-specific immunity levels and transplacental transfer in two successive pregnancies after repeated Tdap-vaccination. Methods: Women enrolled in prior studies on Tdap vaccination during pregnancy were invited to participate in a follow-up study if they became pregnant again. Women who received a Tdap vaccine in both pregnancies were considered for this analysis. Tdap-specific total IgG and IgG subclasses were measured with a multiplex immunoassay. Results: In total, 27 participants with a mean interval between deliveries of 2.4 years were included in the analysis. In maternal serum, Tdap-specific total IgG levels were comparable at both deliveries whereas in cord serum, all Tdap-specific total IgG antibody levels were reduced at the second compared to the first delivery. This was largely reflected in the IgG1 levels in maternal and cord serum. Transplacental transfer ratios of total IgG and IgG1 were also mostly reduced in the second compared to the first pregnancy. Conclusion: This study reports for the first time Tdap-specific total IgG and IgG subclass levels and transfer ratios after repeated Tdap vaccination in successive pregnancies. We found reduced transfer of most Tdap-specific IgG and IgG1 antibodies in the successive pregnancy. As pertussis-specific antibodies wane quickly, Tdap vaccination in each pregnancy remains beneficial. However, more research is needed to understand the impact of closely spaced booster doses during pregnancy on early infant protection against pertussis.

The immune status of migrant populations in Europe and implications for vaccine-preventable disease control: a systematic review and meta-analysis.

BACKGROUND: Ensuring vaccination coverage reaches established herd immunity thresholds (HITs) is the cornerstone of any vaccination programme. Diverse migrant populations in European countries have been associated with cases of vaccine-preventable diseases (VPDs) and outbreaks, yet it is not clear to what extent they are an under-immunized group. METHODS: We did a systematic review and meta-analysis to synthesize peer-reviewed published primary research reporting data on the immune status of migrants in EU/EEA countries, the UK and Switzerland, calculating their pooled immunity coverage for measles, mumps, rubella and diphtheria using random-effects models. We searched on Web of Science, Embase, Global Health and MEDLINE (1 January 2000 to 10 June 2022), with no language restrictions. The protocol is registered with PROSPERO (CRD42018103666). FINDINGS: Of 1103 abstracts screened, 62 met eligibility criteria, of which 39 were included in the meta-analysis. The meta-analysis included 75 089 migrants, predominantly from outside Europe. Pooled immunity coverage among migrant populations was well below the recommended HIT for diphtheria (n = 7, 57.4% [95% confidence interval (CI): 43.1-71.7%] I2 = 99% vs HIT 83-86%), measles (n = 21, 83.7% [95% CI: 79.2-88.2] I2 = 99% vs HIT 93-95%) and mumps (n = 8, 67.1% [95% CI: 50.6-83.6] I2 = 99% vs HIT 88-93%) and midway for rubella (n = 29, 85.6% [95% CI: 83.1-88.1%] I2 = 99% vs HIT 83-94%), with high heterogeneity across studies. INTERPRETATION: Migrants in Europe are an under-immunized group for a range of important VPDs, with this study reinforcing the importance of engaging children, adolescents and adults in 'catch-up' vaccination initiatives on arrival for vaccines, doses and boosters they may have missed in their home countries. Co-designing strategies to strengthen catch-up vaccination across the life course in under-immunized groups is an important next step if we are to meet European and global targets for VPD elimination and control and ensure vaccine equity.

Cost-effectiveness analysis of pertussis booster vaccination for adolescents in Japan.

INTRODUCTION: In Japan, the introduction of a fifth diphtheria-tetanus-acellular pertussis (DTaP) vaccination has been considered, and adolescents aged 11-12 years old who are currently receiving the diphtheria-tetanus (DT) vaccine are one candidate group. We analyze the cost-effectiveness of replacing the DT vaccine with the DTaP vaccine for 11-year-old adolescents and investigate the indirect effect of vaccinated adolescents on unvaccinated infant siblings. We undertake two analyses using high- and low-morbidity pertussis cases, and based on the results, present suggestions for pertussis prevention in the post-COVID-19 pandemic era. METHOD: We used the number of pertussis cases in 2019 as the high-morbidity case and the average number of cases in 2020-2021 as the low-morbidity case, and evaluated the incremental cost-effectiveness ratio (ICER) of the DTaP strategy to the DT strategy based on quality-adjusted life years (QALYs). The economic model contained adolescent and infant sub-models. The indirect effect for infants was considered as the probability of unvaccinated infants avoiding pertussis infection from their vaccinated siblings. RESULTS: The ICER from the payers' perspective was Japanese yen (JPY) 4,254,515 per QALY gained in the high-morbidity case and JPY 62,546,776 per QALY gained in the low-morbidity case. The sensitivity analysis showed that the utility of pertussis had the greatest impact on the ICER, with a 60.58% and 0% probability that the ICER was less than JPY 5 million per QALY gained in the high-morbidity case and low-morbidity case, respectively. CONCLUSION: The cost-effectiveness of replacing the DT vaccine with the DTaP vaccine is affected by the level of pertussis morbidity, with the ICER becoming more favorable in the high-morbidity case. The indirect effect has little impact on the ICER. Thus, policy-makers should continue to monitor the pertussis epidemic in the post-COVID-19 era, and determine the need to introduce a booster based on perceived trends.

A phase 4, open-label study to evaluate the safety and immunogenicity of DTaP5-HBV-IPV-Hib in children previously vaccinated with DTaP2-HBV-IPV-Hib or DTaP5-HBV-IPV-Hib (V419-016).

DTaP5-HBV-IPV-Hib (Vaxelis®) is a hexavalent combination vaccine (HV) indicated in infants and toddlers for the prevention of diphtheria, tetanus, pertussis, hepatitis B, poliomyelitis, and invasive disease due to Haemophilus influenzae type b. Switching between HVs during the childhood vaccination series is sometimes necessary due to, for example, vaccine availability, health-care provider preference, and/or tender awards. The purpose of this study was to describe the safety, tolerability, and immunogenicity of a booster dose of Vaxelis® in participants who previously received a primary infant series of either DTaP2-HBV-IPV-Hib (Hexyon®) or Vaxelis®. Healthy participants approximately 11-13 months of age who previously received a two-dose primary series of Hexyon® (HHV group) or Vaxelis® (VVV group) all received a Vaxelis® booster dose. Immunogenicity was evaluated by measuring antibody levels to individual vaccine antigens approximately 30 days following booster vaccination. Safety was evaluated as the proportion of participants with adverse events (AEs). The proportions of participants with antibody-specific responses for antigens contained in both Vaxelis® and Hexyon® at 30 days post-toddler-booster vaccination with Vaxelis® were comparable between groups, and higher in the VVV group for Vaxelis® antigens PRN and FIM2/3. The overall proportions of participants with AEs were generally comparable between groups. Following a booster dose of Vaxelis®, immune responses were comparable between groups for all shared antigens, and higher in the VVV group for antigens found only in Vaxelis®. The booster was well tolerated in both groups. These data support the use of Vaxelis® as a booster in mixed HV regimens.