GUINEA-BISSAU — Secretary of the Department of Health and Human Services Robert F. Kennedy Jr. cited research by Peter Aaby to justify cutting $2.6 billion in U.S. support for Gavi and freezing an additional $600 million in current funding for the vaccine alliance. Gavi estimated that the $2.6 billion reduction could result in 1.2 million preventable deaths over five years in the world's poorest countries.

"The 2017 paper is a landmark study by five highly regarded mainstream vaccine experts that found that girls who received a diphtheria-tetanus-pertussis shot were 10 times more likely to die from all causes than unvaccinated children," Kennedy said. He froze the $600 million in current Gavi funding citing vaccine safety concerns that have been largely debunked.

The 2017 study included about 500 girls, of whom four vaccinated against DTP in a three-month period died of unrelated causes, while one unvaccinated girl died during that period. Christine Stabell Benn acknowledged that the study was too small to confidently make such assertions. A follow-up study published in 2022 by the same group found that the DTP shot by itself had no effect on mortality.

Aaby spent nearly two decades collecting data on 100,000 residents of Bissau, the capital of Guinea-Bissau. Aaby and Benn said that measles and tuberculosis vaccines derived from live, weakened viruses and bacteria boosted child survival beyond protecting against those pathogens, while vaccines made from deactivated whole germs or pieces of them, such as the diphtheria-tetanus-pertussis shot, caused more deaths—especially among girls—than receiving no vaccine. The World Health Organization repeatedly examined these findings without reaching a conclusion.

In 2023, Aaby and Benn's team wrote that the framework for testing, approving, and regulating vaccines needs to be updated to accommodate non-specific effects. A national scientific board is investigating their work.

Lone Graff Stensballe, a pediatrician at Rigshospitalet in Copenhagen, said she had chosen Guinea-Bissau in 1996 as a research post. She later became critical of the researchers' conclusions. "It took years to see what I see clearly today, that there is a strange concerning pattern in their work," Stensballe said. "Their work is full of confirmation bias," she added.

"They became more strident in saying that their findings were real and that the world needed to do something about it," said Kathryn Edwards, a vaccinologist at Vanderbilt University. "And they became more aligned with RFK."

Danish health authorities have never followed Aaby and Benn's vaccine recommendations and still provide vaccines based on inactivated viruses and bacteria according to their established schedule. On March 16, a federal judge temporarily blocked changes to the U.S. vaccine schedule initiated under Kennedy.