Immunogenicity of fractional one-fifth and one-half doses of 17DD yellow fever vaccine compared with full dose in children aged 9-23 months in Uganda: a phase 4, single-blind, randomised clinical trial.
Reena H Doshi, Irene Lubega, Pierre Muhoza et al.
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In 30 seconds
This phase 4, single-blind, randomised trial compared one-fifth (0·1 mL) and one-half (0·25 mL) with full (0·5 mL) doses of 17DD yellow fever vaccine in children aged 9–23 months at three Ugandan public-sector facilities. Among 1784 randomly assigned children, both fractional doses met the prespecified non-inferiority criterion for seroconversion at 4 weeks. In the per-protocol analysis, the difference between one-half and full doses was -0·17 (95% CI -0·52 to 0·17); no difference was found between one-fifth and full doses. The study supports fractional dosing for outbreak response when vaccine supplies are limited.
Key findings
- Both fractional doses met the 5 percentage-point non-inferiority criterion for seroconversion at 4 weeks compared with the full dose.
- The one-half versus full-dose seroconversion difference was -0·17 (95% CI -0·52 to 0·17) in the per-protocol population.
- No difference in seroconversion was found between one-fifth and full doses.
Why it matters
Evidence in children younger than 2 years has been limited. These randomised findings indicate that reduced 17DD doses can induce initial seroconversion comparable to a full dose in this age group, informing consideration of dose-sparing during yellow fever outbreaks when vaccine supply is constrained.
What to keep in mind
The reported primary result concerns initial seroconversion at 4 weeks; the abstract does not establish longer-term protection.