A planned vaccine trial funded by the US to test hepatitis B shots on 14,000 newborns in Guinea-Bissau has been stopped. The World Health Organization (WHO) called the study "unethical". It wanted some babies to get the vaccine at birth, while others would get it only after six weeks. WHO raised "significant concerns" about this approach. The birth dose vaccine is a proven, life-saving measure used for over 30 years in 115 countries. WHO warned that delaying or withholding this vaccine could cause "potentially irreversible harm" to infants. Guinea-Bissau has a high rate of hepatitis B infection—over 12% of adults and possibly up to 20%. The virus can pass from mother to child at birth. The vaccine prevents this in 70-95% of cases. WHO recommends giving all newborns the vaccine within 24 hours, but Guinea-Bissau currently gives it at six weeks. The government planned to bring birth-dose vaccination nationwide by 2028 but suspended the trial last month after public criticism. Critics, including former health minister Magda Robalo, said, "Guinea-Bissauans are not guinea pigs." The US health department, led by Robert F Kennedy Jr, funded the study and aims to examine broader vaccine effects. Kennedy has questioned vaccine safety before and reshaped US vaccine advisory panels to be more critical. WHO said trials delaying vaccination are only justified when no effective treatment exists, which is not the case here. The agency stressed the ethical issues, scientific validity, and human research standards involved. The halted trial has sparked strong debate over vaccine ethics and public health in Africa.