The World Health Organization has condemned a proposed hepatitis B vaccine trial in Guinea-Bissau, which aimed to enroll thousands of newborns, as "unethical".

The study, backed by the US, intended to administer the vaccine to one group of babies at birth and delay vaccination for another group until they were six weeks old.

According to the WHO, the hepatitis B vaccine given at birth is a crucial public health measure with a proven track record, prompting "significant concerns" about the trial's methodology.

The US Department of Health, led by Robert F Kennedy Jr, had sought to investigate the vaccine's broader health effects through this trial.

On Friday, the WHO expressed concerns regarding the trial's scientific basis, ethical safeguards, and adherence to established human research standards.

With over three decades of use in more than 115 countries, the hepatitis B vaccine has a well-established history of effectiveness.

The WHO argued that withholding a proven life-saving intervention from some newborns could result in "potentially irreversible harm".

Hepatitis B is prevalent in Guinea-Bissau, with a significant portion of the population estimated to be infected; the WHO notes that birth-dose vaccination can prevent mother-to-child transmission in 70-95% of cases.

The WHO maintains that trials involving placebos or withholding treatment are only justifiable when no proven treatment exists, which is not the case with the hepatitis B birth-dose vaccine.

The organization recommends that all newborns receive the hepatitis B vaccine within 24 hours of birth, as infection at birth is the primary cause of lifelong infection, with 90% of infected newborns becoming chronic carriers.

Currently, Guinea-Bissau administers the dose at six weeks, but plans to introduce the birth dose nationwide by 2028, aligning with global standards; the WHO has offered to support this effort.

The suspended trial, led by Danish researchers and funded by the US, had planned to involve 14,000 babies in the West African country.

Public outcry prompted the Guinea-Bissau government to suspend the project last month.

Critics have raised questions about why Guinea-Bissau was chosen as the location for the trial.

In a related development, a US advisory panel recently voted to stop recommending universal hepatitis B vaccination for newborns in the US.

The panel, appointed by US Health Secretary Kennedy, had replaced the previous members of the Advisory Committee on Immunization Practices with new members who have expressed skepticism about vaccines.

Despite denying anti-vaccination views, Kennedy has repeatedly made claims about vaccine harms that have been widely debunked.

Among the vocal opponents of the Guinea-Bissau trial is the country's former health minister, Magda Robalo.

Robalo told the science journal Nature that the trial was "not acceptable" and that "Guinea-Bissauans are not guinea pigs".

According to the WHO, more than 12% of Guinea-Bissau's adult population has chronic hepatitis B, with some studies suggesting the prevalence could be as high as one in five.

Many people with the virus are asymptomatic or experience mild symptoms.

However, some individuals may exhibit jaundice, dark urine, fatigue, nausea, vomiting, and abdominal pain.

The WHO warns that chronic hepatitis B patients are at high risk of developing cirrhosis and liver cancer.

For more news from the African continent, visit BBCAfrica.com.