Low-Dose Yellow Fever Vaccine in Adults in Africa

In this double-blind, randomized, noninferiority trial conducted in Uganda and Kenya, 480 adults with no prior yellow fever vaccination or infection received either the standard dose (13,803 IU) or fractional doses (1000 IU, 500 IU, or 250 IU) of the 17D-204 yellow fever vaccine. The primary outcome was seroconversion (≥4-fold increase in neutralizing antibodies) at 28 days. Seroconversion rates were 98% (95% CI, 94–100) with the standard dose. Differences in seroconversion between fractional doses and the standard dose were:

1000 IU: 0.01 percentage points (95% CI, -5.0 to 5.1)

500 IU: 0.01 percentage points (95% CI, -5.0 to 5.1)

250 IU: -4.4 percentage points (95% CI, -9.4 to 0.7)

Noninferiority (margin: -10 percentage points) was met for the 500-IU and 1000-IU doses. Adverse events were mostly mild and similar across groups. These findings support the use of fractional doses (≥500 IU) as a dose-sparing strategy during yellow fever outbreaks.

In this double-blind, randomized, noninferiority trial conducted in Uganda and Kenya, 480 adults with no prior yellow fever vaccination or infection received either the standard dose (13,803 IU) or fractional doses (1000 IU, 500 IU, or 250 IU) of the 17D-204 yellow fever vaccine. The primary outcome was seroconversion (≥4-fold increase in neutralizing antibodies) at 28 days. Seroconversion rates were 98% (95% CI, 94–100) with the standard dose. Differences in seroconversion between fractional doses and the standard dose were:

1000 IU: 0.01 percentage points (95% CI, -5.0 to 5.1)

500 IU: 0.01 percentage points (95% CI, -5.0 to 5.1)

250 IU: -4.4 percentage points (95% CI, -9.4 to 0.7)

Noninferiority (margin: -10 percentage points) was met for the 500-IU and 1000-IU doses. Adverse events were mostly mild and similar across groups. These findings support the use of fractional doses (≥500 IU) as a dose-sparing strategy during yellow fever outbreaks.