The US-backed hepatitis B vaccine trial in African newborns that drew global backlash was halted, the lead researcher said on Wednesday.

It was “now clear” that the study “will not move forward in Guinea-Bissau”, Frederik Schaltz-Buchholzer, a Danish researcher, wrote on LinkedIn, adding, “we were not given the necessary governmental approval.”

The minister of health in Guinea-Bissau, Quinhin Nantote, previously denied that the project would move forward. “This is not even remotely true,” Nantote told the Guardian in Portuguese last week.

The study was to be funded with $1.6m from the US Centers for Disease Control and Prevention (CDC), along with another $1.6m from private partners like the Bill Ackman-backed Pershing Square Foundation and the Bluebell Foundation.

“The solution is clear here: take the money and vaccinate as many kids as you can,” said Paul Offit, a vaccines expert at the Children’s Hospital of Philadelphia, who sharply criticized the proposed study as unethical.

The government of Guinea-Bissau now has control over the researchers’ vaccines, which they apprehended when they searched the offices of the Bandim Health Project on Monday.

It was vital to support Guinea-Bissau in rolling the immunizations out to all newborns as soon as possible, Offit said. Guinea-Bissau currently plans to offer the universal birth dose in 2028.

The Danish researchers, led by Schaltz-Buchholzer, Christine Stabell Benn and Peter Aaby, hypothesized giving live vaccines, like the Bacillus Calmette-Guérin (BCG), may have an overall mortality benefit beyond simply preventing illnesses like tuberculosis – but giving another vaccine like hepatitis B alongside it could dampen that effect.

Such a hypothesis was “fanciful” because the hepatitis B vaccine is a single protein among billions encountered by the immune system each day, Offit said.

“There’s no evidence for that, and it doesn’t make biological sense,” he continued. He also added that there was a very clear benefit to giving the vaccine to babies as soon as possible, because of high rates of hepatitis B in the country and the possibility of lifelong illness and death from infection.

The Danish researchers did not respond by press time to questions about the study or to this criticism. The CDC did not respond by press time to questions about whether the funding, which was appropriated through its global health work, would now be used to roll out the vaccine to all newborns in Guinea-Bissau, as recommended by the World Health Organization (WHO).

“WHO recommends that all infants receive a first dose of the hepatitis B vaccine as soon as possible after birth – preferably within 24 hours – followed by at least two additional doses,” said Tarik Jašarević, a WHO spokesperson. “WHO remains committed to working with national authorities, researchers, and partners to ensure that all newborns – in Guinea‑Bissau and worldwide – receive timely, evidence‑based protection against hepatitis B.”

Those who declined participation in the study would not have received the vaccines – making true informed consent impossible, experts say.

“Imagine you’re a mother. You want to do the best for your child,” said Henrik Støvring, a Danish researcher who has co-published research raising questions about previous research from the Bandim project.

“If they decide to participate in the trial, they have a 50% chance of getting the vaccine for their children. But if they stay out, they have a 0% chance of getting the vaccine. So how can you say that’s a non-coercive informed consent?” Støvring asked.

The proposed trial led to distrust among Bissau-Guineans, who wondered if the vaccine – which has a decades-long record of being safe and effective – was being tested on Africans because it was dangerous, Schaltz-Buchholzer said in his post.

It “should be clear” that both birth vaccination schedules – with or without hepatitis B – are not “dangerous to anyone”, he wrote. There is a clear benefit to giving hepatitis B vaccines at birth, and not doing so can lead to lifelong danger, experts say.

Conducting a study like this “makes the case that there’s something that’s worthy of study, for which they have no evidence”, Offit said.

“We have millions and millions, arguably hundreds of millions, of children in this world who have gotten that vaccine as a birth dose or haven’t. If there was any evidence that this was problematic, you would know this by now,” Offit added. “We eliminated hepatitis B in the United States in children virtually within years of starting that program, so the benefits are clear.”

Schaltz-Buchholzer also cast doubt on the effectiveness and safety of the hepatitis B vaccine at birth, noting that he believes the study was canceled because it challenges “prevailing medical assumptions, such as that HBV0 does not have non-specific effects”. The study, in addition to looking at mortality, would have also examined side-effects such as skin conditions and neurodevelopmental conditions. Dozens of studies have shown no link between vaccination and autism.

“All newborns should be given a birth dose of hepatitis B vaccine,” Offit said. “Guinea-Bissau is a country that suffers a high incidence of chronic hepatitis B. That country, more than any other country, arguably, needs to launch this program.”