In 2025, a controversy erupted over a study led by the Danish anthropologist Peter Aaby, whose team proposed to investigate the safety of the hepatitis B vaccine, funded by the United States Centres for Disease Control. The objective of the study was an effort to understand its “non-specific vaccine effects” among vaccine eligible children in Guinea-Bissau. That West African country gained independence from Portugal in 1974 after a long war of independence, and has been plagued by significant political unrest and violence ever since, including a civil war between 1998-1999. The hypothesis proposed by the researchers, widely criticised on scientific and ethical grounds, was that the hepatitis B vaccine, developed in 1981 and used successfully for over three decades, may weaken babies’ immune systems or cause neurological disease.
What triggered particular and understandable concern about this study among commentators hinged on its methods. While accounts of “non-specific vaccine effects” generally emerge from observational studies (where findings were not controlled for variables), the study proposed a randomised control trial (RCT), meaning that it would have a placebo or no-treatment arm. In other words, some babies would not be given the hepatitis B birth dose vaccine, which, administered together with immunoglobulin, can prevent chronic hepatitis B infection and resulting liver disease. The ethical problems with the proposed study were evident since it exposed “newborns to serious and potentially irreversible harm, including chronic infection, cirrhosis, and liver cancer.” While the ethics approval for the study was withdrawn by the African Centre for Disease Control in late 2025, the status of this study was not clear in early 2026.
At the core of Aaby’s work is the concept of “non-specific effects” of vaccines against various diseases. The concept is simple — vaccines can have effects on health beyond those intended and beyond the scope of study. This is not in itself an odd idea. Immunologists and virologists puzzle over the various possibilities of different vaccines beyond their intended use. Immunity is complex and research is moving fast. For example, in 2025, the UK government recommended meningococcal B vaccine for the prevention of gonorrhea for gay and other men who have sex with men, although a recent randomized control trial has raised doubts about its effectiveness in this regard.
Most attention has focused on the role Aaby has played in the context of anti-vaccination sentiment in Robert F. Kennedy Jr.’s Health and Human Services. The methodological and ethical problems associated with the proposed study have been dissected and discussed as has the long history of using inequality in access to vaccines as an opportunity for research. Yet this is only part of the story, one that does not understand its context or possibility for emergence. In this post I introduce the life of a concept, that of “non-specific effects,” and trace its travel from the early 1990s to the mid-2020s. The political context into which Aaby’s work enters is the curious mix of the second Trump administration’s defunding of global health, techno-utopian ideology, and protectionism for US industry (including pharmaceutical industry).
I contextualise the boundary work that the concept of “non-specific effects” has played, bringing together different medical, economic, and political actors, forms of scientific evidence, and concepts of risk from the 1990s to the present day. By situating this recent scandal in the context of relevant efforts to live with viruses, I reflect on the limits of “symbiosis” — living together — as a concept that can generate the grounds for reframing health on more ecological terms. Viruses and their emergence and treatment are not only natural events. This makes any recourse to a symbiotic relation with viruses, in which certain viruses are potentially beneficial, naive. This story helps to show how symbiotic thinking can generate unexpected outcomes, including those that contrast with scientific orthodoxy, raising important questions about the meanings of evidence in sustaining prevention as a key platform in late 20th and early 21st century global health.
Hepatitis B vaccination
That vaccination is controversial is no surprise. After all, vaccines, since the development of their rudimentary forerunners in the 18th century, have been about weighing up many possibilities and evaluating potential outcomes — what historian of science Ilana Lowy calls “the history of balancing contradictory aspirations.” Yet how the Hepatitis B vaccine came to be the subject of research funded by the United States Centres for Disease Control speaks to specific histories of vaccination, global health policy, and economic shifts in the late 20th century. In this respect, the Hepatitis B vaccine has an itinerary that is representative of late 20th century vaccinology and virology. Specifically, the intersection of a shift towards preventative medicine in global public health, technological innovation possible by molecular biology, and the commercialization of scientific discovery and its transformation into profitable diagnostics and therapeutics.
The hepatitis B virus causes either chronic or acute liver disease, and in the case of the former, cancer. Most commonly it is transmitted through sexual activity or through blood, including in the latter from mother to child at birth. Post-transfusion hepatitis had plagued the medical establishment since the mid 20th century, when the hepatitis B virus was unknown and undetectable using existing laboratory methods until the identification of its surface antigen, and its first diagnostic methods in 1969. Decades later, the development of a recombinant hepatitis B vaccine in 1986 was groundbreaking, created out of innovations in molecular biology and funded by biotech capital. This prompted patents that restricted its wide distribution, contributing to both an inequality that persists today, as well as efforts to develop alternative vaccine production and distribution in Asia. It was also both the first vaccine for cancer and vaccine for a sexually transmitted disease.
Since the mid-20th century, global health agencies have identified the prevention and treatment of hepatitis as a prominent issue, although it has been overshadowed by the response to HIV/AIDS. Hepatitis B continues to be a significant cause of disease and death, including in Guinea-Bissau. The reasons for this appear to hinge on the disease profile and epidemiology of hepatitis B, in addition to political and economic neglect of this and other infectious disease epidemics. Acute disease (cirrhosis and liver cancer) can occur after the long incubation period and lead to a complete recovery or not. Another reason is perhaps partially due to the fact that widespread vaccination in Western countries in the 1990s diffused the threat that it posed. In many parts of the global south, and particularly in west and central Africa, hepatitis B has been and remains a significant cause of disease and death. To address this, Gavi (the global funding alliance for vaccination against disease), has supported the introduction of new vaccines for children, including Hepatitis B, in several countries, including Guinea-Bissau, from the mid-2000s.
Seeking evidence for the non-specific effects of vaccines
The hepatitis B vaccine was a remarkable achievement yet, like many global health innovations, has failed to live up to its promise, as it is yet to be made available to the world’s poorest countries that have the highest burden of hepatitis B. Yet even in wealthy countries, where it was made widely available, the introduction of the hepatitis B vaccine did not proceed smoothly. In the 1990s in France, where the Pasteur Institute had been implicated in a series of public health scandals including contaminated blood scandal, hepatitis B vaccination was actively promoted to school aged children between 1994 and 1996. While a success, with some 20 million people vaccinated, in 1998 the voluntary vaccination of school aged children was suspended following several case reports of neurological disease following vaccination. These results were not confirmed in epidemiological studies. These lingering and unresolved concerns in the global north, where health has become framed in terms of consumption, has shaped the global political context in which Aaby’s study emerged.
The reason for Aaby’s interest in hepatitis B lies in the demographic and epidemiological profile of the disease caused by the virus. Hepatitis B can be transmitted from mothers to their babies during the birthing process. Where babies born to mothers infected with hepatitis B are not given treatment and vaccination at birth, they are more likely to develop chronic hepatitis B infection and associated disease. While complicated by factors of immune disorders and coinfection (with hepatitis C and HIV, for example), in most cases, adults infected with hepatitis B will clear the virus after an acute infection.
Inconclusive results and vague concerns drove Aaby and his team's proposal. The proposed RCT in 2025, emerged from an observational study of hepatitis B that followed a randomized trial of measles vaccine that took place between 1995 and 2001 in Guinea-Bissau. Across that period, a small cohort of measles vaccine recipients were offered the hepatitis B vaccine schedule at less than 1 year of age. The study investigated whether, as Aaby had hypothesised in the case of measles vaccination, hepatitis B vaccine was associated with sex specific differences in mortality. The study purported to show that hepatitis B vaccination resulted in a higher mortality rate (as many critics have noted, evaluating mortality in childhood is extremely difficult, particularly given disease caused by chronic hepatitis B infection is only likely to emerge many decades later). The authors speculate that, like their suggestion that there are “non-specific vaccine effects” caused by the inactivated polio vaccine after the measles vaccine, the fact that hepatitis B vaccine is inactivated may play a role. Aaby and his team had introduced the hepatitis B vaccine as part of a wider measles vaccination program, which continued throughout the 1990s, with data continuing to be collected during the 1998-1999 civil war. The findings of the study are inconclusive and mostly speculative, but conclude by calling for randomised studies of new vaccines associated with high mortality.
The fact that this investment in a specific form of symbiosis, or coexistence, between different viruses, the body’s immune system, and evidence for health interventions, took place in Africa is no coincidence. West and central Africa are settings where considerable research has been undertaken to understand and track and contain emerging viruses, in addition to being a geographical region with a long history of interventions involving vaccination. In one example, viruses and vaccination come together in the investment in theories of the origins of HIV, in the discredited hypothesis that oral polio vaccines spawned the HIV pandemic, due to the use of a kidney culture containing the simian immunodeficiency virus (from which the most common HIVs are established to have evolved from). This theory followed the widely publicized discovery of a monkey virus, SV40, as a contaminant in early oral polio vaccines. While evidence so far suggests that SV40 does not cause cancer in humans, it did prompt new problems for regulators required to justify the risks associated with preventative vaccines. It introduced the idea that there are contaminants in vaccines meant to be “pure” — one case picked up (given the scale of polio vaccine) by anti-vaccination as a political movement.
Conclusion
The reemergence of the category of “non-specific effects” in a proposed RCT to evaluate hepatitis B in Guinea-Bissau marks a distinctive shift. As is well described, that the CDC would support such research, marks a clear shift both on ethical but also on scientific grounds. This has commonly been referred to in terms of the growing ways that state interventions like vaccines and “anti-vaccination” have become areas of substantial political interest and debate. The consolidation of non-specific effects — and the effort to establish potential harms from vaccines as fact using the gold standard of evidence, requires deeper engagement with “symbiosis.” Hints in Aaby’s other work, and interest in the role of strengthened immune systems resulting from measles infection, highlight this view. At its heart, this work in the field of infectious diseases may be a perspective that runs alongside work on the microbiome, in which “natural” balance is seen as a corrective to excessive biomedical interventions.
However, this controversy prompts important reflections on the meanings of scientific evidence and interventions in health. An RCT is obviously not a suitable method with which to evaluate a vaccine that is established to be safe, particularly in a setting where hepatitis B is endemic. It is not to say that non-specific effects associated with vaccines are not possible, and that the history of medical interventions is not a worthy area of study. Rather, what is important to question is why an RCT, which puts at high risk the health of children, would be the selected mode of evidence — and not, say, the tools of history, anthropology, and epidemiology. These disciplinary tools would also help to develop a different conceptual language of symbiosis, one that centers material encounters between bodies of different species, different viruses and other agents, diagnostics, vaccines, treatments, and the technologies that facilitate their development and distribution.
To understand this process requires an approach that includes addressing the virology of history, an account of the history of diverse medical and non-medical interventions into and using viruses. But even more important — and almost entirely missing in the furore that surrounded this proposed study — was the perspectives of parents of children and people living with hepatitis B in Guinea-Bissau. After all, it is in the bodies of children and their parents in Guinea-Bissau and elsewhere that retain the traces of mid-century interventions and many failures of global health. A view of the virology of history that accounts for the perspective of those whose access to healthcare depends on regimes of scientific studies in the guise of humanitarianism, can yield new perspectives on the reemergence of symbiosis in the context of major economic, political, scientific and medical shifts in the contemporary world.
Published: 07/27/2026