Vaccine · 2026
Persistence of immune responses 5 years after vaccination with a single dose of typhoid conjugate vaccine (TCV) in Nepalese children.
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Pant Dikshya, Zhang Yiyuan, Feaheny Francesca, Kim Young Chan, Shakya Mila, Shrestha Suchita, Curtis Benjamin, Dongol Sabina, Shrestha Sonu, Gehlhaar Arne, Gurung Meeru, Mujadidi Yama F, Kelly Sarah, Haque Naheeda, Joshi Manij, Maharjan Archana, Dahal Ashata, Rijal Suraj, Subhani Huma, Karkey Abhilasha, Basnyat Buddha, Shrestha Shrijana, Pollard Andrew J, Liu Xinxue, TyVAC Nepal Study Team
Аннотация
BACKGROUND: A single-dose typhoid conjugate vaccine (TCV) has been recommended in endemic settings. Here we report the 5-year immunogenicity results post a single dose of TCV in Nepal.
METHODS: We conducted a participant- and observer-blinded randomised trial (RCT) in Lalitpur, Nepal (2017-2021) (ISRCTN43385161). 20,019 children aged 9 months to ≤16 years were randomised to receive Typbar TCV (Vi-TT; Bharat Biotech International, India) or capsular group A meningococcal conjugate vaccine (MenA) in 2017-2018. After unblinding in 2020-2021, children were offered the alternate vaccine and were followed until 2025. A subgroup of 1500 participants (1000 Vi-TT, 500 MenA) were recruited into the immunogenicity cohort, who had blood samples taken at Day 0, Day 28, Month 18, Years 2, 4, and 5 post-baseline. The primary outcome is anti-Vi antibody responses.
RESULTS: The median age at TCV vaccination was 10.1 in the 2017/2018 cohort and 13.1 in the 2020/2021 cohort. The geometric mean concentration (GMC) of anti-Vi IgG was 2037.90 (95% CI: 1904.86-2180.23) at Day 28, dropping to 241.29 (220.27-264.31) at Month 18. At Year 5 post-vaccination, the GMC was 109.3 (98.65-121.10). The proportion of participants maintaining a ≥4-fold rise at Year 5 post-vaccination from baseline remained high (88%). Antibody decay was significantly slower in older children, females, and children with detectable baseline anti-Vi IgG, compared with their respective reference groups. Anti-Vi IgA was highly correlated with IgG (p < 0.0001).
CONCLUSIONS: This study provides evidence that anti-Vi immunity is sustained for at least 5 years post-vaccination. Children vaccinated at younger ages showed a faster decline, highlighting the need for further investigation into the optimal age for vaccination and the need for boosters.
FUNDING: Wellcome Trust.
METHODS: We conducted a participant- and observer-blinded randomised trial (RCT) in Lalitpur, Nepal (2017-2021) (ISRCTN43385161). 20,019 children aged 9 months to ≤16 years were randomised to receive Typbar TCV (Vi-TT; Bharat Biotech International, India) or capsular group A meningococcal conjugate vaccine (MenA) in 2017-2018. After unblinding in 2020-2021, children were offered the alternate vaccine and were followed until 2025. A subgroup of 1500 participants (1000 Vi-TT, 500 MenA) were recruited into the immunogenicity cohort, who had blood samples taken at Day 0, Day 28, Month 18, Years 2, 4, and 5 post-baseline. The primary outcome is anti-Vi antibody responses.
RESULTS: The median age at TCV vaccination was 10.1 in the 2017/2018 cohort and 13.1 in the 2020/2021 cohort. The geometric mean concentration (GMC) of anti-Vi IgG was 2037.90 (95% CI: 1904.86-2180.23) at Day 28, dropping to 241.29 (220.27-264.31) at Month 18. At Year 5 post-vaccination, the GMC was 109.3 (98.65-121.10). The proportion of participants maintaining a ≥4-fold rise at Year 5 post-vaccination from baseline remained high (88%). Antibody decay was significantly slower in older children, females, and children with detectable baseline anti-Vi IgG, compared with their respective reference groups. Anti-Vi IgA was highly correlated with IgG (p < 0.0001).
CONCLUSIONS: This study provides evidence that anti-Vi immunity is sustained for at least 5 years post-vaccination. Children vaccinated at younger ages showed a faster decline, highlighting the need for further investigation into the optimal age for vaccination and the need for boosters.
FUNDING: Wellcome Trust.