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Objective: To determine the seroprevalence of antibodies against of diphtheria, tetanus, and pertussis among Thai adolescents. Methods: A cross-sectional study was conducted among Thai adolescents aged 11–20 years who had completed five doses of diphtheria, tetanus, and pertussis (DTP)-containing vaccine during childhood, either diphtheria toxoid, tetanus toxoid, whole-cell pertussis (DTwP) or diphtheria toxoid, tetanus toxoid, acellular pertussis (DTaP) vaccine. Protective antibodies against diphtheria, tetanus, and pertussis were defined as anti-diphtheria toxoid IgG ≥0.1 IU/ml, anti-tetanus toxoid IgG ≥0.1 IU/ml, and anti-Bordetella pertussis toxin IgG ≥5 IU/ml, respectively. Results: Of 220 adolescents (median age 16 years), 45% had received a tetanus toxoid, reduced diphtheria toxoid (Td) booster vaccine during adolescence, and none (0%) had received a tetanus toxoid, reduced diphtheria toxoid, acellular pertussis (Tdap) booster vaccine. Overall, 50%, 99%, and 57% of adolescents demonstrated protective antibodies against diphtheria, tetanus, and pertussis, respectively. The geometric mean concentrations (GMCs) of antibodies against diphtheria (p = 0.06) and tetanus (p < 0.001) were higher among adolescents who had received Td vaccine. Nevertheless, the antibody levels against both diseases waned over time, regardless of Td booster vaccination. Likewise, pertussis antibody levels gradually declined after the fifth childhood dose of DTwP/DTaP vaccine. Conclusions: Approximately half of these healthy Thai adolescents had not maintained protective antibodies against diphtheria and pertussis. A booster vaccination with diphtheria toxoid and/or acellular pertussis-containing vaccines is a crucial strategy to prevent such diseases in this population.

Background To determine the prevalence and associated factors of seroprotection against Japanese encephalitis (JE) virus among HIV-infected adolescents stable on combination antiretroviral treatment (cART). Methods A multicenter seroprevalence study was conducted in Thailand. Perinatally HIV-infected adolescents who aged 11–25 years, had previous evidence of severely immune suppression (CD4 < 15% or < 200 cells/mm3), were currently stable on cART (CD4 > 350 cells/mm3 for > 6 months or CD4 > 200 cells/mm3 with viral suppression [VS; plasma HIV RNA < 50 copies/mL] for > 12 months), and had completed a 3- or 4-dose series of mouse brain-derived inactivated JE vaccine (MBDV) during childhood were enrolled. Adolescents who had clinically or serologically confirmed recent JE virus infections, or received immunosuppressive agents or blood components within 6 months were excluded. Plaque reduction neutralization (PRNT50) assay was conducted to assess neutralizing antibodies to JE virus, and titers of ≥ 10 were considered seroprotective. Logistic regression analysis was performed to identify associated factors of JE seroprotection. Results Of 98 eligible adolescents, 54% were female, a median age was 19 years, and 11% were overweight. Ninety-five percent and 5% of adolescents received 3 and 4 doses of MBDV during childhood, respectively. A median duration since the last dose of MBDV was 16 years. At enrollment, 71% were on NNRTI-based cART regimens, a median cART duration was 13 years. A median current CD4 was 29%, and 89% had VS. Seroprotection against JE virus was identified in 28 (29%) adolescents; of whom, the geometric mean titer (GMT) of neutralizing antibody was 64 (95% CI: 39–106). Proportion of adolescents with JE seroprotection and GMT of neutralizing antibodies to JE virus slightly decreased over time after the last immunization (Figure 1). In a multivariable logistic regression analysis, seroprotection against JE virus was associated with younger age and greater current CD4 count (Table 1). Conclusion The majority of our perinatally HIV-infected adolescents did not maintain seroprotection against JE virus although having completed a series of MBDV during childhood. JE revaccination is an important tool for disease prevention in these adolescents who live in JE endemic areas. Disclosures All authors: No reported disclosures.

Background To assess the prevalence and associated factors of protective antibodies against diphtheria, tetanus, and pertussis among HIV-infected adolescents stable on combination antiretroviral treatment (cART). Methods A multicenter seroprevalence study was conducted. Perinatally HIV-infected Thai adolescents (11–25 years) who had previous evidence of severely immune suppression (CD4 < 15% or < 200 cells/mm3), were currently stable on cART (CD4 > 350 cells/mm3 for > 6 months or CD4 > 200 cells/mm3 with viral suppression [VS; HIV RNA < 50 copies/mL] for > 12 months) and had completed a 5-dose series of diphtheria, tetanus, whole cell pertussis (DTwP) vaccine during childhood were enrolled. Adolescents who received immunosuppressive agents or blood components within 6 months were excluded. Protective antibodies for diphtheria, tetanus, and pertussis were defined as diphtheria toxoid IgG ≥ 0.1 IU/mL, tetanus toxoid IgG ≥ 0.1 IU/mL, and anti-pertussis toxin IgG ≥ 5 IU/mL, respectively. Logistic regression analysis was performed to identify factors associated with protective antibody response to each antigen. Results Of 150 adolescents, 47% were male, a median age was 19 years. Forty (27%) and 0 (0%) adolescents had ever received tetanus, diphtheria (Td) or tetanus, diphtheria, acellular pertussis (Tdap) vaccine during adolescence, respectively. A median duration since the last dose of DTwP/Td vaccine was 12 years. At enrollment, 67% of adolescents were on NNRTI-based cART regimens, a median cART duration was 13 years. A median CD4 was 29%, and 90% had VS. Prevalence of protective antibodies against diphtheria, tetanus, and pertussis were 37%, 82%, and 52%, respectively. Proportion of adolescents with protective antibodies and geometric mean concentrations of antibodies to all antigens declined over time after the last immunization (Figures 1–3). Associated factors of protective antibodies to diphtheria, tetanus and pertussis are shown in Table 1. Conclusion Although having completed a 5-dose series of DTwP during childhood, significant proportion of our perinatally HIV-infected adolescents had no protective antibodies to those antigens, particularly diphtheria and pertussis, when entering adolescence. Tdap vaccination is a crucial strategy to prevent such diseases in the future. Disclosures All authors: No reported disclosures.