Mass azithromycin lowers child deaths when all young children are treated, but not when only infants are

The World Health Organization's 2020 guideline recommended giving mass azithromycin, which lowers child mortality in high-mortality settings of sub-Saharan Africa, only to infants, to limit antibiotic resistance; no trial had then tested that. Under a pre-registered plan we pooled every randomized trial by whom it treated. Treating all children under five lowered their mortality by 14.1% (CI 7.4% to 20.3%), consistently across trials. In the three trials that treated only infants, infant mortality was not detectably lower (rate ratio 0.971, CI 0.867 to 1.086), an interval that excludes the effect of treating all children. Infants had lower mortality when all children were treated, though a between-trial comparison of the two strategies fell short of significance, and giving azithromycin to individual infants at clinic visits showed no effect. The infant-only approach has not lowered mortality in any trial that tested it; treating all children under five has.