Vaccination: why don’t we all experience the same side effects?

A team from UNIGE and HUG reveals why some people develop more pronounced transient symptoms following mRNA vaccination against COVID-19

Université de Genève

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Redness and pain at the injection site, fever, fatigue or headaches: vaccines can cause side effects, but their frequency and severity vary considerably from person to person. Why? A team from the Center for Vaccinology at the University of Geneva (UNIGE) and Geneva University Hospital (HUG) has found that, even before vaccination, some people’s innate immune systems are more reactive than others, showing a heightened response to interferons, key molecules involved in antiviral defence naturally produced by the body. The stronger this response, the more likely individuals are to experience these transient symptoms. These findings have been published in Science Translational Medicine.

The reactions experienced by some people after vaccination are, in most cases, mild and temporary. They result from activation of the immune system by the vaccine, enabling the body to learn to recognise antigens – characteristic molecules of the virus present in the vaccine – and thereby prepare to better fight off any future infection. This activation can cause local inflammation at the injection site (redness and swelling) or more peripheral symptoms such as fatigue or fever. However, the response varies considerably from person to person, ranging from no reaction at all to pronounced flu-like symptoms.

“Whilst we know that older people tend to experience fewer reactions to vaccination because of age-related declines in immune function, and that the vaccine dose can influence the severity of side effects, the biological mechanisms underlying these individual differences in symptoms have remained poorly understood,” explains Arnaud Didierlaurent, Associate Professor at the Center for Vaccinology (UNIGE/HUG) and in the Department of Pathology and Immunology at the Faculty of Medicine, UNIGE.

The role of our immune ‘‘capital’’

To investigate these differences, the researcher and his team monitored the immune systems of 51 healthy individuals recruited at HUG who received two doses of an mRNA vaccine against COVID-19. As side effects generally occur one to two days after vaccination, particularly after the second dose, participants were monitored for seven days following each injection.

“This study allowed us to identify an important role for an interferon-related antiviral defence system in explaining differences in side effects between individuals. This innate immune defence system helps us, in particular, to fight viral infections. The more active a person’s natural interferon response is, even before vaccination, the more pronounced their reactions to vaccination are likely to be,” explains Natacha Madelon, Senior Research and Teaching Assistant at the Center for Vaccinology and first author of the study.

Interferon is produced by cells when they are infected with a virus, alerting neighbouring cells and preparing them to defend themselves. But not everyone starts from the same ‘baseline’. “For reasons we do not yet fully understand – but which may be linked to genetic factors, a particular microbiome or a previous inflammatory episode – some individuals have a stronger  interferon-related immune signature before receiving the vaccine, which appears to influence how strongly they react to vaccination,” explains Arnaud Didierlaurent.

Differences emerge after the second dose

The research team identified a second potential mechanism in an animal model. Following the first vaccination, the body develops antibodies and T cells capable of recognising the vaccine antigen. When a subsequent dose is administered, this acquired immunity can rapidly amplify the activation of certain innate immune cells, notably monocytes, a type of white blood cell. These cells then react more strongly, attracting more inflammatory cells to the injection site.

These findings open up new avenues for vaccine research. In particular, they suggest that it may eventually be possible to better distinguish between the mechanisms needed to generate a robust immune response and those that primarily contribute to the symptoms experienced following vaccination. Prof. Didierlaurent’s team is now seeking to determine whether these same mechanisms occur with other types of vaccines.

In the long term, this research could contribute to the development of vaccines that are better tolerated while remaining just as effective. “In any case, a mild reaction, or even the absence of symptoms following vaccination, does not in any way mean that the vaccine is ineffective. The severity of side effects is therefore not, in itself, an indicator of how well a vaccine is working” concludes Arnaud Didierlaurent.

This research was supported by the HUG Private Foundation, the Giorgio Cavaglieri Foundation and Moderna.

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Journal

Science Translational Medicine

DOI

10.1126/scitranslmed.aee4776

Method of Research

News article

Subject of Research

Not applicable

Article Title

Baseline interferon signaling in monocytes and antibody-mediated innate activation are associated with reactogenicity to mRNA vaccines

Social media spreading misleading claims about Alzheimer’s blood tests, study finds

Many posts omitted limitations, harms and appropriate use of testing

University of Sydney

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Researchers have raised concerns about the promotion of Alzheimer’s disease blood tests on social media, particularly posts making claims that do not align with current clinical recommendations. 

 

In the first published study of its kind, researchers from the University of Sydney analysed 188 posts shared between March 2014 and May 2025 on Facebook, Instagram and TikTok about Alzheimer’s blood tests, which have been allowed in Australia since July this year. Posts came from accounts with a combined audience of more than 114 million followers. 

 

Published in the Journal of the American Geriatrics Society, the study found more than a third of posts suggested the tests could be used to screen healthy people without symptoms of cognitive decline, despite current recommendations against routine testing of asymptomatic people.

 

Lead author Dr Jenna Smith from the University of Sydney’s School of Public Health and the Sydney Health Literacy Labsaid the findings come at a time of growing public interest in Alzheimer’s blood tests, including their recent introduction in Australia. 

 

“Social media is presenting exciting claims about what these new blood tests might be able to do, but that excitement can outpace the evidence,” she said.

 

“We know people turn to social media for health information. When content leaves out important context about who these tests are for, their limitations and potential downsides, there’s a risk people may develop unrealistic expectations or seek testing that isn’t recommended for them.”

 

The blood tests are intended to support diagnosis of Alzheimer’s disease in people experiencing cognitive decline. The researchers found 59 percent of posts promoted the tests as useful for earlier or improved diagnosis, however many failed to mention that clinical assessment remains essential or that the tests are only recommended for people experiencing symptoms.

 

Only 36 percent of posts included evidence supporting their claims, and fewer than one quarter of those cited a specific study. The analysis also found accounts with explicit financial interests were more than three times as likely to promote testing for people without symptoms. 

 

Dr Smith said the omission of important information was concerning given the potential consequences of testing people who are otherwise healthy. The study found posts discussing testing for healthy people rarely mentioned potential harms, such as overdiagnosis, false positive results or the broader impacts an Alzheimer’s diagnosis can have on individuals and families.

 

“Dementia is one of the most feared health conditions among adults,” she said. 

 

“Understandably, people want answers and may be drawn to new tests that appear to offer certainty or early detection. But for people without symptoms, there’s currently no evidence that screening provides a benefit. 

 

“A positive result may create anxiety and uncertainty, particularly when there is no cure for Alzheimer’s disease and guidance on how these new tests should be used is still evolving.

 

“People with no symptoms could be diagnosed with Alzheimer’s disease but not go on to develop dementia that impacts their life.”

 

Dr Smith said the findings highlight the need for clear, evidence-based information to help people understand who may benefit from testing and what the results can and cannot tell them. 

 

“These tests may play an important role in supporting diagnosis for some people experiencing cognitive symptoms, but they should be interpreted with appropriate clinical oversight,” she said. 

 

“It’s important that consumers are getting balanced information rather than relying on social media alone. Posts should always include advice to speak with a health professional before undertaking any Alzheimer’s blood testing.”

 

The researchers say clinicians should also be aware of how social media may shape public perceptions of Alzheimer’s blood tests. They are calling for improved regulatory enforcement and resources to support conversations about the benefits, limitations and uncertainties surrounding testing. 

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Journal

Journal of the American Geriatrics Society

DOI

10.1111/jgs.70692

Method of Research

Content analysis

Subject of Research

People

Article Title

Social media claims about blood tests for Alzheimer’s disease and dementia: A cross-sectional content analysis

Article Publication Date

16-Sep-2026

Wildfire smoke may be more harmful than other air pollution, two Mount Sinai studies find

Wildfire-related PM2.5 linked to higher hospitalization risks for cardiovascular and respiratory disease and poorer survival among people with lung cancer

The Mount Sinai Hospital / Mount Sinai School of Medicine

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NEW YORK, NY (September 17, 2026)– As climate change drives more frequent and intense wildfires, researchers at the Icahn School of Medicine at Mount Sinai have published two large-scale studies showing that wildfire smoke may pose greater health risks than other sources of air pollution, with higher risks of hospitalization for cardiovascular and respiratory disease and poorer survival among patients with lung cancer.

The studies, led by first author Min Zhang, PhD, and senior author Yaguang Wei, PhD, provide some of the strongest evidence to date that the source of air pollution matters, not just the amount.

Published in Nature Communications and The Lancet Oncology, the studies examined the long-term health effects of fine particulate matter from wildfires, known as PM2.5, a mixture of microscopic airborne particles that can penetrate deep into the lungs and enter the bloodstream. Across both investigations, the researchers found that wildfire-related PM2.5 was associated with greater health risks per unit of exposure than PM2.5 from non-wildfire sources.

The findings come as wildfire smoke increasingly affects communities far beyond traditional fire-prone regions, exposing tens of millions of people across the United States to elevated levels of air pollution.

“Wildfire smoke is no longer a regional environmental issue. It is becoming a nationwide public health challenge,” said Dr. Wei, Assistant Professor, Environmental Medicine, Icahn School of Medicine at Mount Sinai, and senior author of both studies. “Our research shows that wildfire-related PM2.5 appears to be more harmful than equivalent levels of pollution from other sources. As wildfire activity increases, public health and environmental policies must account for both the quantity and the source of air pollution.”

Wildfire Smoke Associated With Reduced Survival Among Patients With Lung Cancer

The first study, published September 15 in The Lancet Oncology, examined whether long-term exposure to wildfire-related PM2.5 affects survival among patients with lung cancer. Researchers analyzed data from 414,016 adults aged 65 years and over with lung cancer in the SEER-Medicare database. They estimated patients’ wildfire-related and non-wildfire PM2.5 exposure based on where they lived, using total ambient PM2.5 estimates developed on their own and wildfire-specific PM2.5 estimates published by researchers at Stanford University.

The study found that both wildfire-related and non-wildfire PM2.5 were associated with increased mortality risk among patients following lung cancer diagnosis. However, when researchers compared equivalent increases in exposure, wildfire-related PM2.5 was associated with substantially greater toxicity: although wildfire-related PM2.5 accounts for only about 4 percent of total PM2.5, it is responsible for about 17 percent of mortality related to total PM2.5 exposure. The findings suggest that long-term exposure to wildfire smoke may be an important and previously underrecognized risk factor for patients with lung cancer.

Among study participants, researchers estimated that hundreds of annual deaths were attributable to wildfire-related PM2.5 exposure. They also found that higher numbers of smoky days and prolonged periods of smoke exposure were associated with poorer survival outcomes.

“Patients with lung cancer are already medically vulnerable, and our findings suggest that wildfire smoke may place them at even greater risk,” said Dr. Zhang. “As wildfire-related air pollution becomes more common, reducing exposure could become an increasingly important component of cancer care and survivorship planning.”

According to Dr. Wei, the findings have immediate implications for clinicians and patients.

“For people with lung cancer or chronic heart and lung diseases, monitoring air quality and limiting exposure during smoke events may be especially important,” Dr. Wei said. “Health care providers may increasingly need to consider environmental exposures as part of comprehensive patient care.”

“Lung cancer patients are already navigating substantial health challenges, and our findings suggest that long-term exposure to wildfire smoke may add another, potentially preventable risk.” said Christine Ekenga, PhD, MPH, Rollins Assistant Professor at Emory University’s Rollins School of Public Health and co-author of the study. “We need to better understand which patients are most vulnerable and develop practical strategies to reduce their exposure.”

Wildfire Smoke Linked to Increased Risks of Heart and Lung Disease Hospitalizations

In the second study, published September 17 in Nature Communications, investigators analyzed hospitalization records from residents across 20 U.S. states between 2006 and 2019 and linked them to advanced models estimating long-term exposure to wildfire-related and non-wildfire PM2.5. The study included more than 57 million cardiovascular hospitalizations and nearly 33 million pulmonary disease hospitalizations.

Researchers found that long-term exposure to wildfire-related PM2.5 was associated with increased risks of hospitalization for a broad range of cardiovascular and respiratory conditions, including heart failure, ischemic heart disease, hypertension, asthma, pneumonia, chronic obstructive pulmonary disease, and other respiratory illnesses. At equivalent concentrations, wildfire-related PM2.5 was consistently associated with larger increases in hospitalization risk than PM2.5 from non-wildfire sources.

“This study provided a unique opportunity to directly compare the health impacts of wildfire smoke with other sources of air pollution on a large scale,” said Dr. Zhang, postdoctoral fellow in the Department of Environmental Medicine at the Icahn School of Medicine at Mount Sinai and first author of both studies. “We found that wildfire smoke can affect both the lungs and the cardiovascular system, and that its effects may be stronger than those of similar amounts of pollution from traffic, industry, and other sources.”

The researchers also found particularly strong associations among racial and ethnic minority populations, residents of metropolitan areas, and people living in communities with lower educational attainment and higher levels of socioeconomic deprivation.

The study was conducted by investigators from the Icahn School of Medicine at Mount Sinai, Harvard T.H. Chan School of Public Health, Stony Brook University, and New York University and was supported by the National Institute of Environmental Health Sciences

Implications for Public Health and Future Research

Taken together, the studies suggest that wildfire smoke should be considered a distinct environmental health threat requiring targeted mitigation strategies beyond traditional approaches focused on overall air pollution levels. Future research will focus on identifying which chemical components of wildfire smoke are responsible for its heightened toxicity and understanding the biological mechanisms through which wildfire-related PM2.5 affects cardiovascular health, respiratory disease, and cancer outcomes.

“As wildfire activity continues to grow around the world, understanding the health consequences of wildfire smoke has become increasingly urgent,” said Dr. Wei. “These studies represent an important step toward identifying who is most vulnerable and what strategies may help protect public health in a changing climate.”

Journal Information

The Lancet Oncology
Long-term exposure to wildfire-related PM2.5 and overall survival of older patients with lung cancer: a retrospective, registry-based cohort study
Published September 15, 2026.

Nature Communications
Cardiopulmonary hospitalization risks from wildfire and non-wildfire PM2.5 in 20 US states
Published September 17, 2026.

Funding

The Nature Communications study was supported by the National Institute of Environmental Health Sciences under grant numbers P30ES023515, R01ES036566, and UL1TR004419.

The Lancet Oncology study was supported by the National Institute of Environmental Health Sciences, the National Cancer Institute, the National Institutes of Health, the National Center for Advancing Translational Sciences, the Centers for Disease Control and Prevention’s National Program of Cancer Registries, Emory University, and Stony Brook University.

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About the Mount Sinai Health System

Mount Sinai Health System is one of the nation’s leading integrated academic health systems and one of the largest in the New York metropolitan area. Its comprehensive system includes seven hospitals, more than 400 outpatient practices, over 600 research and clinical laboratories, the Icahn School of Medicine at Mount Sinai, the Graduate School of Biomedical Sciences, and the Mount Sinai Phillips School of Nursing. Together, the Health System comprises approximately 48,000 employees, more than 9,000 physicians, and 8,600 nurses.

As a leading learning health system, Mount Sinai combines clinical expertise with scientific discovery to improve patient care while training the next generation of health care and biomedical leaders. The Health System provides care across every stage of life, from prenatal care through geriatrics, while advancing personalized medicine through artificial intelligence, data science, and biomedical research.

Mount Sinai is consistently recognized among the nation’s leading academic health systems for patient care, research, and education. The Mount Sinai Hospital is ranked No. 1 in New York by Newsweek and No. 5 on the magazine’s World’s Best Hospitals list. The Icahn School of Medicine at Mount Sinai ranks No. 11 among U.S. medical schools and No. 1 among freestanding medical schools for National Institutes of Health funding, reflecting the strength of its scientific enterprise and leadership in biomedical research. 

 Australia

Hidden caves beneath the Nullarbor revealed by subtle surface

Curtin University

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image: 

Nullarbor Plain cave interior

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Credit: Matej Lipar

Mysterious trenches stretching for kilometres across southern Australia’s Nullarbor Plain have been revealed as the surface footprints of deep, hidden ancient cave systems.

 

New research involving Curtin University has found that shallow, sediment-filled trenches formed when underground caves gradually collapsed, eventually reaching the surface. This challenges the idea that they were carved out by flowing water, as their appearance might suggest.

 

The findings provide a new way to identify hidden cave systems in dry landscapes on Earth and could help scientists interpret similar features on Mars and other planetary surfaces.

 

Lead author Dr Matej Lipar, who at the time of the research was an Adjunct Research Fellow in Curtin’s School of Earth and Planetary Sciences, and is now at the Anton Melik Geographical Institute at the Research Centre of the Slovenian Academy of Sciences and Arts (ZRC SAZU), said the trenches were difficult to recognise as evidence of underground caves because their surface features were so subtle.

 

“From the surface, these features can look remarkably like shallow valleys or drainage channels, but our evidence shows they have a very different origin,” Dr Lipar said.

 

“By combining mapping, geophysical surveys, cave records and sediment analysis, we found these trenches are linked to deep cave systems beneath the Nullarbor Plain.

 

“Over time, the cave roofs progressively collapsed causing sagging of overlying material, eventually creating shallow depressions at the surface.”

 

Dr Lipar said the trenches can range from several kilometres to more than 20 kilometres long and are generally 100 to 500 metres wide, but at less than nine metres deep are hard to see on the huge expanse of the Nullarbor Plain.

 

“Because the landscape is so vast, it appears to be a flat, endless plain. But when we created exaggerated digital models of the terrain, the trenches became much easier to see and identify.” Dr Lipar said.

 

“Unlike typical valleys, the trenches don’t have connected streams or other signs that water once flowed through them. Instead, geophysical surveys found deep underground cavities, while several trenches lined up with known caves and areas where the ground has collapsed.”

 

The researchers also identified a progression from obvious cave-connected collapse features in the west to wider, more subtle trenches further east, showing how cave collapse can progressively reach the surface depending on the thickness of rock.

 

Curtin co-author Associate Professor Milo Barham, from the Curtin Frontier Institute for Geoscience Solutions (CFIGS) and School of Earth and Planetary Sciences, said the findings could change how scientists interpret similar subtle landscape features elsewhere.

 

“Cave systems are not always obvious from the surface, but the dry and stable landscape of the Nullarbor is excellent for removing a lot of “noise” to allow us to recognise subtle landscape characteristics,” Associate Professor Barham said.

 

“This gives us a useful set of indicators for identifying hidden cave systems elsewhere – including on other planets such as Mars.

 

“Caves are important as they can preserve evidence of past environments on Earth and impact our engineering and access to clean drinking water, while potential caves on other planets could provide protected subsurface environments relevant to the search for evidence of extraterrestrial life or act as bases for future astronauts.”

 

The study was supported by the Slovenian Research and Innovation Agency and also involved researchers from The University of Western Australia, La Trobe University, the University of Ljubljana, and The University of Queensland.

 

The full study, ‘Subdued surface expression of deep cave collapse’, was published in Communications Earth and Environment (DOI 10.1038/s43247-026-04016-7).

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Journal

Communications Earth & Environment

Nullarbor Plain cave opening

Researchers explore underground cave

Credit

Matej Lipar

DOI

10.1038/s43247-026-04016-7

Method of Research

Imaging analysis

Subject of Research

Not applicable

Article Title

Subdued surface expression of deep cave collapse

Article Publication Date

17-Sep-2026

Chimpanzees give youngsters the tools to learn tricky techniques

Adult chimpanzees deliberately create learning opportunities for infants by handing over tools

Frontiers

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Two-thirds of a century after Jane Goodall observed ‘David Greybeard’ break off a twig to fashion a fishing rod for termites, researchers following in her footsteps have found that adult chimpanzees in Senegal literally hand youngsters the tools for learning.

Darwin noted in 1871 that chimpanzees use stones to crack nuts, striking a blow to human hubris. Over the 20th century, a select few animals as diverse as octopuses and parrots have been observed making and using tools. But in agreement with Darwin’s observation, tool use seems to have evolved more frequently among monkeys and apes. For example, chimpanzees are known to manufacture leaf sponges to soak up liquids, shape sticks to fish for algae, and sharpen simple spears for hunting.

“Here we show that receiving food and tools from experienced individuals, which we call food or tool transfer, may help chimpanzees learn to use technology to extract foods that are difficult to access,” said Andreu Sánchez-Megías, a PhD candidate at the University of Barcelona and the Jane Goodall Institute Spain in Senegal, who is the first author of a new study in Frontiers in Psychology.

“Tool transfers thus appear to be a form of teaching, together with observation and supervised practice. It appears that mothers are the main models and teachers for young chimpanzees in this manner.”

Share and share alike

Sánchez-Megías and colleagues from the Jane Goodall Institute Spain in Senegal and the University of Barcelona studied wild western chimpanzees (Pan troglodytes verus) at the savanna site of Dindefelo, Senegal. They analyzed almost 15 hours of footage from camera traps taken between 2017 and 2025. The traps had been deliberately installed at 14 spots where chimpanzees were known to use tools, including fishing for algae, army ants, and fungus-growing termites. They also gathered 30 minutes of footage from cameras at 11 sites where chimpanzees habitually carry baobab fruit, which they pound against stationary stone ‘anvils’. While termite fishing and ant dipping occur in communities of all four chimpanzee subspecies across Africa, fishing for algae and ‘baobab pounding’ are known only from western chimpanzees in Senegal, Mali, and Guinea.

Overall, the authors recorded 33 instances of tool transfer from one chimpanzee to another, as well as four where they handed over fruit. The researchers compared the behavior before and after these donations, from both the initial ‘possessors’ and the ‘recipients’ to whom the first handed these objects.

Of the 33 transfers observed, 58% happened in the context of ant dipping, while 30% and 12% took place during algae fishing and termite fishing, respectively. Most (58%) of the original owners were adults, especially females. In contrast, the greatest percentage (42%) of the recipients were infants rather than youngsters or adults. The majority of objects were handed over from one relative to another, most frequently (30%) by mother to her offspring. All but one voluntary transfer seemed to happen at the recipient’s initiative. In some cases, tools and fruit were stolen outright, in which case the unlucky possessor might hit the thief to retaliate or grab the object back.

Unique footage of newly discovered behavior

Importantly, the authors presented two fascinating videos – respectively of ant dipping and baobab pounding – in their study, which for the first time allow other scientists and the general public to watch how such seemingly deliberate ‘technological transfers’ proceed in Dindefelo chimpanzees.

In the first, taken in 2018, mother Soukki deliberately inserted a dipping stick into an ant colony, grabbed her baby daughter Saïsaï, and led it to the ready-to-be-extracted tool. Saïsaï then pulled it from the nest and went on to eat the ants sticking to it. In the second video from 2021, mother Féré collected three fruits. An unidentified juvenile male ‘teacher’ then approached, who proceeded to pick up one fruit and repeatedly pound it against a rocky outcrop, then guided Fotti’s hand to it once. The video shows clearly how Fotti attentively observed the juvenile’s movements and proceeded to try his hand at pounding for himself – eventually with success.

The authors found that the majority of tool transfers took place from skilled to inexperienced individuals, including mothers-offspring pairs and other relatives.

“Teaching is one of the strategies that chimpanzees use to transfer information and skills between individuals. It requires an active role from the teacher, who must modify their behavior to facilitate the transmission of information to the learner, and this is why teaching is thought to have evolved to transfer information that is too complex to be acquired through simpler mechanisms, such as individual or observational learning,” summarized Sánchez-Megías.

”One question that needs to be answered is the extent to which teaching contributes to the transmission of technological behaviors in great apes. Other questions are whether more complex behaviors require more teaching, and whether the individuals that receive more teaching ultimately become better teachers themselves,” said Prof R. Adriana Hernandez-Aguilar, the study’s senior author and the research co-director of the Jane Goodall Institute Spain, as well as Serra Hunter Professor at the University of Barcelona.

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Journal

Frontiers in Psychology

DOI

10.3389/fpsyg.2026.1868894

Method of Research

Observational study

Subject of Research

Animals

Article Title

Savanna chimpanzee tool and fruit transfers facilitate the transmission of technological behaviors at Dindefelo, Senegal

Article Publication Date

16-Sep-2026

COI Statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest

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The Part Played by Labour in the Transition from Ape to Man

This article was intended to introduce ... it, nor even this intro, which breaks off at the end. It would be included in Dialectics of Nature....