Post-Vaccination Yellow Fever Immunity in Infants Receiving Azithromycin in Sierra Leone: Results from a Randomized, Placebo-Controlled, Double-Blind Trial
1
Maternal Newborn Child and Reproductive health, Barcelona Institute for Global Health, Barcelona, Spain
2
Faculty of Medicine and Health Sciences, Universitat de Barcelona, Barcelona, Spain
3
Department of Biostatistics, Barcelona Institute for Global Health, Barcelona, Spain
4
Department of Virology, Hospital Clinic de Barcelona, Barcelona, Spain
5
Barcelona Institute for Gloabl Health, Barcelona, Spain
6
University of Barcelona, Universitat de Barcelona, Barcelona, Spain
7
Consorcio de Investigación Biomédica en Red de Epidemiología y Salud Pública, Epidemiología y Salud Pública, Barcelona, Spain
Popul. Med. 2026;8(Supplement Supplement 1):A3940
ABSTRACT
BACKGROUND:
A single-dose yellow fever (YF) vaccination is recommended for lifelong protection, yet gaps in coverage and limited immunity data contribute to recurrent outbreaks in Africa1-3. This study assessed YF post-vaccination neutralizing antibody titers(NAb), seroconversion rates, and factors associated with low immunogenicity among infants in Sierra Leone.
METHODS:
A nested prospective study in a randomized, placebo controlled, double-blind clinical trial was conducted between March and October 2024, to evaluate the potential effect of oral azithromycin co-administration on immunogenicity of measles, rubella and yellow fever vaccines in Bombali and Tonkolili districts4. Infants aged 9 to <12months with caretaker consent and no prior history of vaccination were included. Peripheral venous blood sample (1mL) were collected before vaccination and drug administration, and one to three months post interventions. NAb were measured by microneutralization (TCID₅₀); seroprotection was ≥ 1:5-1:10 and seroconversion as four-fold increase5. Univariate and multivariate logistic regression were performed.
RESULTS:
Of the 152 infants included, 76 received azithromycin and 76 received placebo. The median age at enrolment was 9 months (IQR: 9.0-9.7) and 12 months (IQR: 12.0-12.7) at the second contact post-vaccination. At a mean time of 87 days(±16.6) post-vaccination, 38 (25%) infants were seropositive and 60 (39.5%) had seroconverted. Non-seroconvertors were predominantly males (58.2%), Bombali residents (57.1%) and had normal nutritional status (71.4%). Seroconversion rates did not differ between study groups. Although no clinical-demographic factors were statistically significant, age, history of hospitalization and outpatient care and receipt of an additional measles, rubella vaccine dose were consistently associated with higher odds of non-seroconversion in the models built.
CONCLUSIONS:
The high proportion of seronegativity and failure to seroconvert raises concerns regarding vaccine failure, including biological factors, potential immune interference and other programmatic factors3,6-8. These findings indicate that many vaccinated children in infancy remain susceptible to YF infection, supporting reconsideration of a booster dose.
A single-dose yellow fever (YF) vaccination is recommended for lifelong protection, yet gaps in coverage and limited immunity data contribute to recurrent outbreaks in Africa1-3. This study assessed YF post-vaccination neutralizing antibody titers(NAb), seroconversion rates, and factors associated with low immunogenicity among infants in Sierra Leone.
METHODS:
A nested prospective study in a randomized, placebo controlled, double-blind clinical trial was conducted between March and October 2024, to evaluate the potential effect of oral azithromycin co-administration on immunogenicity of measles, rubella and yellow fever vaccines in Bombali and Tonkolili districts4. Infants aged 9 to <12months with caretaker consent and no prior history of vaccination were included. Peripheral venous blood sample (1mL) were collected before vaccination and drug administration, and one to three months post interventions. NAb were measured by microneutralization (TCID₅₀); seroprotection was ≥ 1:5-1:10 and seroconversion as four-fold increase5. Univariate and multivariate logistic regression were performed.
RESULTS:
Of the 152 infants included, 76 received azithromycin and 76 received placebo. The median age at enrolment was 9 months (IQR: 9.0-9.7) and 12 months (IQR: 12.0-12.7) at the second contact post-vaccination. At a mean time of 87 days(±16.6) post-vaccination, 38 (25%) infants were seropositive and 60 (39.5%) had seroconverted. Non-seroconvertors were predominantly males (58.2%), Bombali residents (57.1%) and had normal nutritional status (71.4%). Seroconversion rates did not differ between study groups. Although no clinical-demographic factors were statistically significant, age, history of hospitalization and outpatient care and receipt of an additional measles, rubella vaccine dose were consistently associated with higher odds of non-seroconversion in the models built.
CONCLUSIONS:
The high proportion of seronegativity and failure to seroconvert raises concerns regarding vaccine failure, including biological factors, potential immune interference and other programmatic factors3,6-8. These findings indicate that many vaccinated children in infancy remain susceptible to YF infection, supporting reconsideration of a booster dose.
| eISSN: | 2654-1459 |
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