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Background. In the absence of an efficacious broadly protective vaccine, serogroup B Neisseria meningitidis (MenB) is the leading cause of bacterial meningitis and septicemia in many industrialized countries. An investigational recombinant vaccine that contains 3 central proteins; Neisserial adhesin A (NadA), factor H binding protein (fHBP) and Neisserial heparin binding antigen (NHBA) has been developed. These antigens have been formulated with and without outer membrane vesicles (rMenB+OMV and rMenB, respectively) from the New Zealand epidemic strain (B:4:P1.7–2,4). In this trial, we assessed the immunogenicity of these formulations in infants, who are at greatest risk of contracting MenB disease. Methods. A total of 147 infants from the United Kingdom were enrolled and randomly assigned to receive rMenB or rMenB+OMV at 2, 4, 6, and 12 months of age or a single dose at 12 months of age. Serum samples taken before and after vaccination were assayed in a standardized serum bactericidal antibody assay against 7 MenB strains. Local and systemic reactogenicity were recorded for 7 days after each vaccination. Analysis was according to protocol. Results. After 3 doses, both vaccines were immunogenic against strains expressing homologous or related NadA and fHBP. rMenB+OMV demonstrated greater immunogenicity than did rMenB and was immunogenic against strains expressing homologous PorA. Both vaccines elicited anamnestic responses after the fourth dose. For both vaccines, responses were lower against strains expressing heterologous fHBP variants and after a single dose at 12 months. Conclusions. The rMenB+OMV vaccine has the potential to protect infants from MenB disease, although the breadth of protection afforded to heterologous antigens requires additional investigation.

Streptococcus pyogenes (group A Streptococcus, Strep A) is a widespread pathogen that continues to pose a significant threat to human health. The development of a Strep A vaccine remains an unmet global health need. One of the major vaccine strategies is the use of M protein, which is a primary virulence determinant and protective antigen. Multivalent recombinant M protein vaccines are being developed with N-terminal M peptides that contain opsonic epitopes but do not contain human tissue cross-reactive epitopes. We completed a Phase I trial of a recombinant 30-valent M protein-based Strep A vaccine (Strep A vaccine, StreptAnova™) comprised of four recombinant proteins containing N-terminal peptides from 30 M proteins of common pharyngitis and invasive and/or rheumatogenic serotypes, adjuvanted with aluminum hydroxide. The trial was observer-blinded and randomized in a 2:1 ratio for intramuscular administration of Strep A vaccine or an alum-based comparator in healthy adult volunteers, at 0, 30 and 180 days. Primary outcome measures were assessments of safety, including assays for antibodies that cross-reacted with host tissues, and immunogenicity assessed by ELISA with the individual vaccine peptides and by opsonophagocytic killing (OPK) assays in human blood. Twenty-three Strep A-vaccinated participants and 13 controls completed the study. The Strep A vaccine was well-tolerated and there was no clinical evidence of autoimmunity and no laboratory evidence of tissue cross-reactive antibodies. The vaccine was immunogenic and elicited significant increases in geometric mean antibody levels to 24 of the 30 component M antigens by ELISA. Vaccine-induced OPK activity was observed against selected M types of Strep A in vaccinated participants that seroconverted to specific M peptides. The Strep A vaccine was well tolerated and immunogenic in healthy adults, providing strong support for further clinical development. [ClinicalTrials.gov NCT02564237].

Increasing incidence rates, insufficient effectiveness of exposure prevention strategies, and the potential for serious outcomes despite antibiotic treatment highlight the need for a preventive vaccine against Lyme borreliosis. VLA15, an investigational Lyme borreliosis vaccine based on outer surface protein A (OspA) variants from clinically relevant Borrelia burgdorferi sensu lato genospecies in North America and Europe, has shown safety and immunogenicity in adults when administered with various three-dose schedules. We aimed to investigate the safety and immunogenicity of two-dose and three-dose schedules of VLA15 within a broader population, including children and adolescents, who are among those at increased risk of Lyme borreliosis. This randomised, observer-blind, placebo-controlled phase 2 trial is taking place at 14 clinical study centres in Lyme borreliosis-endemic areas in the USA. Healthy, eligible participants aged 5–65 years were enrolled in a 2:1:1 ratio to age cohorts of 18–65 years, 12–17 years, and 5–11 years through a staggered age-descending enrolment process. Within each age cohort, participants were randomly assigned with an electronic data capture system in a 1:1:1 ratio to receive intramuscular injections of 180 μg VLA15 at months 0, 2, and 6 (VLA15 M0-2-6 group); 180 μg VLA15 at months 0 and 6, and placebo at month 2 (VLA15 M0-6 group); or placebo at months 0, 2, and 6. Unmasked individuals included site staff and clinical research associates involved in randomisation and handling the investigational product, as well as specific individuals, both internal and external to the sponsor, who regularly reviewed trial safety data (including statisticians preparing relevant tables). All other individuals were masked; unmasking after the database snapshot for month 7 analyses for each age cohort was limited to the trial sponsor, collaboration partner, and statisticians. The primary immunogenicity endpoint was OspA serotype (ST)-specific IgG geometric mean titres (GMTs) assessed by ELISAs at month 7 (ie, 1 month after the third vaccination) and was evaluated in the per-protocol analysis set. The primary safety endpoint was the frequency of solicited local and systemic adverse events occurring within 7 days after each and any vaccination and were assessed in the safety analysis set (ie, all individuals who received at least one vaccination). This report includes safety and immunogenicity data through to month 12. This trial is ongoing but no longer recruiting participants, and is registered with Clinicaltrials.gov (NCT04801420). Between March 15, 2021, and Feb 24, 2022, 625 participants (321 [51%] female, 304 [49%] male) received one or more vaccinations and were included in the safety analysis set. Of these, 190 participants were included in the VLA15 M0-2-6 group, 187 were included in the VLA15 M0-6 group, and 208 were included in the placebo group; 40 additional VLA15 recipients could not be allocated to either VLA15 group because their vaccination schedules were non-compliant with both VLA15 groups due to missed or incorrect vaccinations; however, these individuals were included in safety analyses. OspA-specific ELISA IgG GMTs at month 7 in the overall population (aged 5–65 years) were significantly higher in the VLA15 M0-2-6 group (333·2 [95% CI 275·2–403·4; ST1] to 656·0 [560·2–768·2; ST2] units per mL) and VLA15 M0-6 group (197·3 [156·2–249·3; ST1] to 460·3 [370·6–571·8; ST2] units per mL) compared with the placebo group (21·9 [20·2–23·7; ST2] to 24·3 [22·1–26·7; ST6] units per mL; p<0·0001 for all comparisons); GMTs were also significantly higher in the VLA15 M0-2-6 group than in the VLA15 M0-6 group (all p<0·0001 except for ST2 [p=0·0010] and ST3 [p=0·011]). Among VLA15 recipients, GMTs were highest in children followed by adolescents and then adults. Solicited local adverse events after any vaccination occurred more frequently among VLA15 recipients (M0-2-6, 178 [94%; 95% CI 89–96] of 190; M0-6, 176 [94%; 90–97] of 187) than placebo recipients (71 [34%; 28–41] of 208; p<0·0001 for both comparisons); the same was true for solicited systemic adverse events (M0-2-6, 128 [67%; 95% CI 60–74] of 190, p=0·0015 vs placebo; M0-6, 128 [68%; 61–75] of 187, p=0·0007 vs placebo; placebo, 107 [51%; 45–58] of 208). Most solicited adverse events were mild or moderate in severity; none was grade 4. There were no significant differences in the frequencies of unsolicited adverse events, related unsolicited adverse events, unsolicited serious adverse events (serious adverse events), and adverse events of special interest across groups in the overall population. None of the severe unsolicited adverse events, serious adverse events, or adverse events of special interest were considered related to vaccination and no deaths occurred through to month 12 of the trial. These findings confirm previously observed safety and immunogenicity profiles of VLA15 in adults and extend them to children aged 5 years and older and adolescents. The greater immunogenicity of VLA15 among children and adolescents might translate to increased flexibility in the real-world clinical setting. Pfizer and Valneva.

Incidence rates of Lyme borreliosis, a tickborne disease attributed to infection by Borrelia species, are increasing, and limitations to existing treatments potentiate the possibility of severe outcomes. Nevertheless, there are no licensed vaccines for Lyme borreliosis prevention in humans. This study investigated the immunogenicity and safety of a booster dose of VLA15, an investigational outer surface protein A (OspA)-based Lyme borreliosis vaccine that has previously shown safety and immunogenicity when administered as a primary vaccination series, following a primary VLA15 vaccination series. We report the results of the booster phase of a randomised, observer-blinded, placebo-controlled, multicentre, phase 2 study that enrolled healthy adults aged 18–65 years from five US clinical study centres to receive 135 μg or 180 μg VLA15 or placebo at months 0, 2, and 6 in the main study phase. Participants who received 180 μg VLA15 in the main study phase and did not have relevant protocol deviations were eligible for the booster phase (months 18–30). Participants were randomly reassigned (2:1) to receive an intramuscular injection of a VLA15 booster or placebo 1 year after the completion of primary vaccination (month 18) via a randomisation list generated by an unmasked statistician with a block size of six. Individuals involved in data safety monitoring, rerandomisation, vaccine handling, and vaccine accountability were unmasked; the study sponsor and statisticians were only unmasked after analysis of data up to 1 month after booster administration. All other individuals remained masked throughout the booster phase. The outcomes for the booster phase were the immunogenicity (evaluated in the booster per-protocol population) and safety (evaluated for all participants who received the booster) of the booster dose up to month 30. The study is registered at ClinicalTrials.gov (NCT03970733) and is completed. Between Feb 4 and March 23, 2021, 58 participants (28 men and 30 women) were screened, randomly assigned, and received VLA15 (n=39) or placebo (n=19). One participant in the placebo group was lost to follow-up. The IgG geometric mean titres for each OspA serotype (serotypes 1–6) in the VLA15 group peaked at 1 month after the booster dose (1277·0 U/mL [95% CI 861·8–1892·3] to 2194·5 U/mL [1566·8–3073·7] vs 23·6 U/mL [18·1–30·8] to 36·8 U/mL [26·4–51·3] in the placebo group [p<0·0001 for all serotypes]), remained elevated at month 24 (137·4 U/mL [95·8–196·9] to 265·8 U/mL [202·9–348·2] vs 22·3 U/mL [17·7–28·0] to 29·1 U/mL [20·8–40·6] in the placebo group; p<0·0001 for all serotypes), and declined by month 30 (54·1 U/mL [38·6–75·7] to 101·6 U/mL [77·6–133·1] vs 21·9 U/mL [18·0–26·6] to 24·9 U/mL [19·0–32·6] in the placebo group; p<0·0001 for all serotypes except serotype 1 [p=0·0006]). Solicited local adverse events were reported more frequently in the VLA15 group (35 [92%, 95% CI 79–97] of 38 participants) than the placebo group (six [32%, 15–54] of 19 participants; p<0·0001) after booster vaccination. There was no significant difference in the frequency of solicited systemic adverse events between groups (20 [59%, 42–74] of 34 participants in the VLA15 group vs six [38%, 18–61] of 16 participants in the placebo group). Related unsolicited adverse events (none severe) were reported by two (5%, 1–17) of 39 participants in the VLA15 group and none (0%, 0–17) of 19 participants in the placebo group. There were no severe solicited local or systemic adverse events or deaths during the study. A booster dose of VLA15 is safe and induces substantial anamnestic immune responses against all six OspA serotypes. As with previously investigated OspA-based Lyme borreliosis vaccines, waning immune responses were observed with VLA15, and annual boosters might therefore be required. Valneva.

Rising Lyme borreliosis incidence rates, potential for severe outcomes, and limitations in accurate and timely diagnosis for treatment initiation suggest the need for a preventive vaccine; however, no vaccine is currently available for human use. We performed two studies in adults to optimise the dose level and vaccination schedule for VLA15, an investigational Lyme borreliosis vaccine targeting outer surface protein A (OspA) serotypes 1–6, which are associated with the most common pathogenic Borrelia species in Europe and North America. Both randomised, observer-blind, placebo-controlled, multicentre phase 2 studies included participants aged 18–65 years without recent history of Lyme borreliosis or tick bites. Study one was conducted at nine clinical research and study centre sites in the USA (n=6), Germany (n=2), and Belgium (n=1); study two was conducted at five of the study one US sites. Based on a randomisation list created by an unmasked statistician for each study, participants were randomly assigned via an electronic case report form randomisation module to receive 90 μg (study one only), 135 μg, or 180 μg VLA15 or placebo by intramuscular injection at months 0, 1, and 2 (study one) or 0, 2, and 6 (study two). Study one began with a run-in phase to confirm safety, after which the Data Safety Monitoring Board recommended the removal of the 90 μg group and continuation of the study. In the study one run-in phase, randomisation was stratified by study site, whereas in the study one main phase and in study two, randomisation was stratified by study site, age group, and baseline B burgdorferi (sensu lato) serostatus. All individuals were masked, other than staff involved in randomisation, vaccine preparation or administration, or safety data monitoring. The primary endpoint for both studies was OspA-specific IgG geometric mean titres (GMTs) at 1 month after the third vaccination and was evaluated in the per-protocol population. Safety endpoints were evaluated in the safety population: all participants who received at least one vaccination. Both studies are registered at ClinicalTrials.gov (study one NCT03769194 and study two NCT03970733) and are completed. For study one, 573 participants were screened and randomly assigned to treatment groups between Dec 21, 2018, and Sept, 26, 2019. For study two, 248 participants were screened and randomly assigned between June 26 and Sept 3, 2019. In study one, 29 participants were assigned to receive 90 μg VLA15, 215 to 135 μg, 205 to 180 μg, and 124 to placebo. In study two, 97 participants were assigned to receive 135 μg VLA15, 100 to 180 μg, and 51 to placebo. At 1 month after the third vaccination (ie, month 3), OspA-specific IgG GMTs in study one ranged from 74·3 (serotype 1; 95% CI 46·4–119·0) to 267·4 units per mL (serotype 3; 194·8–367·1) for 90 μg VLA15, 101·9 (serotype 1; 87·1–119·4) to 283·2 units per mL (serotype 3; 248·2–323·1) for 135 μg, and 115·8 (serotype 1; 98·8–135·7) to 308·6 units per mL (serotype 3; 266·8–356·8) for 180 μg. In study two, ranges at 1 month after the third vaccination (ie, month 7) were 278·5 (serotype 1; 214·9–361·0) to 545·2 units per mL (serotype 2; 431·8–688·4) for 135 μg VLA15 and 274·7 (serotype 1; 209·4–360·4) to 596·8 units per mL (serotype 3; 471·9–754·8) for 180 μg. Relative to placebo, the VLA15 groups had more frequent reports of solicited local adverse events (study one: 94%, 95% CI 91–96 vs 26%, 19–34; study two: 96%, 93–98 vs 35%, 24–49 after any vaccination) and solicited systemic adverse events (study one: 69%, 65–73 vs 43%, 34–52; study two: 74%, 67–80 vs 51%, 38–64); most were mild or moderate. In study one, unsolicited adverse events were reported by 52% (48–57) of participants in the VLA15 groups and 52% (43–60) of those in the placebo groups; for study two these were 65% (58–71) and 69% (55–80), respectively. Percentages of participants reporting serious unsolicited adverse events (study one: 2%, 1–4; study two: 4%, 2–7) and adverse events of special interest (study one: 1%, 0–2; study two: 1%, 0–3) were low across all groups. A single severe, possibly related unsolicited adverse event was reported (worsening of pre-existing ventricular extrasystoles, which resolved after change of relevant concomitant medication); no related serious adverse events or deaths were reported. VLA15 was safe, well tolerated, and elicited robust antibody responses to all six OspA serotypes. These findings support further clinical development of VLA15 using the 180 μg dose and 0-2-6-month schedule, which was associated with the greatest immune responses. Valneva.

Background Group A streptococci (Strep A) or Streptococcus pyogenes is a major human pathogen causing an estimated 500,000 deaths worldwide each year. Disease can range from mild pharyngitis to more severe infections, such as necrotizing fasciitis, septicemia, and toxic shock syndrome. Untreated, Strep A infection can lead to the serious post streptococcal pathologies of rheumatic fever/rheumatic heart disease and post-streptococcal glomerulonephritis. An effective vaccine against Strep A would have great benefits worldwide. Here, we test two products, J8 and p*17—both peptide derivatives of a highly conserved region in the M protein, in combination with the protein subunit K4S2 of SpyCEP, an IL-8 protease associated with neutrophil chemoattraction. Each peptide is individually conjugated to cross reacting material (CRM 197 ), and the conjugated peptide vaccines are abbreviated as J8-K4S2 or p*17-K4S2. Methods This single-site phase I, two-stage clinical trial in Edmonton, Alberta, Canada, aims to recruit a total of 30 healthy volunteers, aged 18–45 years, without any evidence of pre-existing valvular heart disease. The trial is divided into the initial unblinded safety test dose stage (stage 1) and the randomized, double-blinded, controlled trial stage (stage 2). Stage 1 will recruit 10 volunteers—5 each to receive either J8-K4S2 or p*17-K4S2 in an unblinded, staggered fashion, whereby volunteers are dosed with intentional spacing of at least 2 days in between doses to monitor for any immediate side effects before dosing the next. Once all 5 volunteers have received 3 doses of the first test vaccine, a similar process will follow for the second test vaccine. Once safety is established in stage 1, we will proceed to stage 2, which will recruit 20 volunteers to our 3-arm randomized controlled trial (RCT), receiving either of the trial vaccines, J8-K4S2 or p*17-K4S2, or comparator (rabies) vaccine. All product dosing will be at 0, 3, and 6 weeks. The primary outcome is vaccine safety; the secondary outcome is immunogenicity and comparative analyses of the different vaccine regimens. Discussion This Strep A vaccine clinical trial aims to investigate safety and immunogenicity of two novel conjugated peptide-based vaccines, J8-KS42 and p*17-K4S2. If one or both vaccine products demonstrate favorable primary and secondary outcomes, the product(s) will move into phase II and III studies. Trial registration ClinicalTrials.gov Identifier: NCT04882514. Registered on 2021–05-12, https://clinicaltrials.gov/study/NCT04882514 .

Lyme borreliosis is caused by Borrelia burgdorferi sensu stricto in the USA and by several Borrelia species in Europe and Asia, but no human vaccine is available. We investigated the safety and immunogenicity of adjuvanted and non-adjuvanted vaccines containing protective epitopes from Borrelia species outer surface protein A (OspA) serotypes in healthy adults. Between March 1, 2011, and May 8, 2012, we did a double-blind, randomised, dose-escalation phase 1/2 study at four sites in Austria and Germany. Healthy adults aged 18–70 years who were seronegative for B burgdorferi sensu lato were eligible for inclusion. Participants were recruited sequentially and randomly assigned to one of six study groups in equal ratios via an electronic data capture system. Participants and investigators were masked to group allocation. Participants received three vaccinations containing 30 μg, 60 μg, or 90 μg OspA antigen with or without an adjuvant, with intervals of 28 days, and a booster 9–12 months after the first immunisation. The coprimary endpoints were the frequency and severity of injection-site and systemic reactions within 7 days of each vaccination, and the antibody responses to OspA serotypes 1–6, as established by ELISA. This study is registered with ClinicalTrials.gov, number NCT01504347. 300 participants were randomly assigned: 151 to adjuvanted vaccines (50 to 30 μg, 51 to 60 μg, and 50 to 90 μg doses), and 149 to non-adjuvanted vaccines (50 to 30 μg, 49 to 60 μg, and 50 to 90 μg doses). Adverse reactions were predominantly mild, and no vaccine-related serious adverse events were reported. The risk of systemic reactions (risk ratio 0·54 [95% CI 0·41–0·70]; p<0·0001) and of moderate or severe systemic reactions (0·35 [0·13–0·92]; p=0·034) was significantly lower for adjuvanted than non-adjuvanted formulations. The 30 μg adjuvanted formulation had the best tolerability profile; only headache (five [10%, 95% CI 4–20] of 50), injection-site pain (16 [32%, 21–45]), and tenderness (17 [34%, 23–47]) affected more than 6% of patients. All doses and formulations induced substantial mean IgG antibody titres against OspA serotypes 1–6 after the first three vaccinations (range 6944–17 321) and booster (19 056–32 824) immunisations. The 30 μg adjuvanted formulation induced the highest antibody titres after the booster: range 26 143 (95% CI 18 906–36 151) to 42 381 (31 288–57 407). The novel multivalent OspA vaccine could be an effective intervention for prevention of Lyme borreliosis in Europe and the USA, and possibly worldwide. Larger confirmatory formulation studies will need to be done that include individuals seropositive for Borrelia burgdorferi sensu lato before placebo-controlled phase 3 efficacy studies can begin. Baxter.

Vaccination against complex pathogens such as typhoidal and non-typhoidal Salmonella requires the concerted action of different immune effector mechanisms. Outer membrane proteins (Omps) of Salmonella Typhi are potent immunogens, which elicit long-lasting and protective immunity. Here, we followed the evolution of S. Typhi OmpC and F-specific T and B cell responses in healthy volunteers after vaccination with the vaccine strain Ty21a. To follow humoral and cellular immune responses, pre- and post-vaccination samples (PBMC, serum and stool) collected from 15 vaccinated and 5 non-vaccinated individuals. Immunoglobulin levels were assessed in peripheral blood by enzyme-linked immunosorbent assay. B cell and T cell activation were analyzed by flow cytometry. We observed a significant increase of circulating antibody-secreting cells and maximal Omp-specific serum IgG titers at day 25 post vaccination, while IgA titers in stool peaked at day 60. Likewise, Omp-specific CD4+ T cells in peripheral blood showed the highest expansion at day 60 post vaccination, concomitant with a significant increase in IFN-γ and TNFα production. These results indicate that S. Typhi Omp-specific B cell responses and polyfunctional CD4+ T cell responses evolve over a period of at least two months after application of the live attenuated vaccine. Moreover, these findings underscore the potential of S. Typhi Omps as subunit vaccine components. ISRCTN18360696.

This phase 1 clinical trial assessed the safety and immunogenicity of a native outer membrane vesicle (NOMV) vaccine prepared from a lpxL2(−) synX(−) mutant of strain 44/76 with opcA expression stabilized. Thirty-four volunteers were assigned to one of the three dose groups (25 mcg, 25 mcg with aluminum hydroxide adjuvant, and 50 mcg) to receive three intramuscular injections at 0, 6 and 24 weeks. Specific local and systemic adverse events (AEs) were solicited by diary and at visits on days 1, 2, 7 and 14 after each vaccination and at the end of the study at 30 weeks. Blood chemistries, complete blood count, and coagulation studies were measured on each vaccination day and again two days later. Blood for antibody measurements and bactericidal assays were drawn 0, 14, and 42 days after each vaccination. The proportion of volunteers who developed a fourfold or greater increase in serum bactericidal activity (SBA) to the wild-type parent of the vaccine strain with high opcA expression at 6 weeks after the third dose was 12/26 (0.46, 95% confidence interval 0.27–0.65). Antibody levels to OpcA were significantly higher in vaccine responders than in non-responders ( p = 0.008), and there was a trend for higher antibody levels to the lipooligosaccharide (LOS) ( p = 0.059). Bactericidal depletion assays on sera from volunteers with high-titer responses also indicate a major contribution of anti-OpcA and anti-LOS antibodies to the bactericidal response.These results suggest that genetically modified NOMV vaccines can induce protection against group B meningococcus.

Infants are at greatest risk for pertussis morbidity and mortality. Maternal vaccination during pregnancy has been shown to prevent pertussis in young infants in high- and middle-income countries. However, data on the levels of maternal pertussis antibodies and the efficiency of transplacental transfer in low-income South Asian settings are limited. To estimate the prevalence of maternal pertussis antibodies and the efficiency of transplacental transfer in rural southern Nepal. Paired maternal-infant blood samples were collected from a subsample of participants in a randomized, controlled trial of maternal influenza immunization (n=291 pairs). Sera were tested by enzyme-linked immunosorbent assays for pertussis toxin, filamentous hemagglutinin, pertactin, and fimbriae. Maternal and infant pertussis antibody levels and transplacental transfer efficiency were determined and potential factors associated with both were assessed. Elevated maternal antibodies to pertussis toxin, suggesting recent pertussis infection, were rarely detected (4%, tested n=305). However, paired maternal-cord sera were highly correlated across all antibodies; transplacental antibody transfer ratios for pertussis toxin were 1.14 (n=291, 95% CI 1.07–1.20); filamentous hemagglutinin 1.10 (n=120, 95% CI: 1.01–1.20); fimbriae 2/3 1.05 (n=120, 95% CI: 0.96–1.15) and pertactin 0.96 (n=289, 95% CI: 0.91–1.00). Older gestational age was associated with increased pertussis toxin and decreased fimbriae 2/3 antibody transport. A low prevalence of maternal antibody to all four pertussis antigens was noted in Nepal, but transplacental antibody transfer was efficient. No consistent demographic factors were associated with elevated maternal antibody levels or efficiency of transplacental transfer. If an increase in infant pertussis disease burden was detected in this population, maternal immunization could be an effective intervention to prevent disease in early infancy.