---
title: "Why some people have stronger vaccine side effects: immune signaling and what to do"
id: "medical-news-today-0-vaccines-why-some-of-us-are-more-likely-to-experience-side-effects-and-what-to"
canonical_url: "https://medichelpline.com/clinical-feed/medical-news-today-0-vaccines-why-some-of-us-are-more-likely-to-experience-side-effects-and-what-to"
content_type: "clinical_feed_article"
specialty: "Infectious Disease"
source_name: "Medical News Today"
source_url: "https://www.medicalnewstoday.com/articles/vaccines-why-some-people-more-likely-experience-side-effects-what-to-do/"
published_at: "2026-10-01T12:00:00.000Z"
evidence_level: "Verified Feed"
license: "CC-BY-NC-4.0 / Informational Use"
---
# Why some people have stronger vaccine side effects: immune signaling and what to do
## Provenance & Clinical Metadata
- **Canonical URL:** https://medichelpline.com/clinical-feed/medical-news-today-0-vaccines-why-some-of-us-are-more-likely-to-experience-side-effects-and-what-to
- **Specialty:** [Infectious Disease](https://medichelpline.com/clinical-feed/infectious-disease.md)
- **Primary Source:** Medical News Today
- **Source URL:** [Original Journal Publication](https://www.medicalnewstoday.com/articles/vaccines-why-some-people-more-likely-experience-side-effects-what-to-do/)
- **Published At:** 2026-10-01T12:00:00.000Z
- **Evidence Rating:** Verified Feed
## Executive GIST (TL;DR)
- A Swiss team from the Center for Vaccinology at the University of Geneva (UNIGE) and Geneva University Hospital (HUG) studied why some individuals report stronger short-term reactions after seasonal vaccination, using COVID-19 mRNA vaccines as a case study. - The study combined observations from 51 healthy adult human participants (median age 43.5 years) who received two mRNA vaccine doses and experiments in mouse models. - Researchers monitored participants for one week after each dose to record side effects and measured immune activity. - The investigators identified differences in an **interferon**-related antiviral signaling pathway as a likely explanation for individual variability in vaccine reactions. - Individuals with a more active baseline interferon response tended to report more pronounced post-vaccination symptoms. - In mice, acquired immunity after the first vaccine dose amplified responses of other immune cells, notably **monocytes**, after the second dose, which can intensify reactions. - The study authors and an independent GP noted that vaccine reactions were generally mild and temporary and that stronger side effects do not indicate better vaccine effectiveness. - There is currently no validated way to predict or prevent these immune responses; standard symptomatic measures — rest, hydration, and paracetamol where appropriate — are recommended. - The study did not identify any group who should avoid seasonal vaccines; only those with concerns about serious allergic reactions to vaccine ingredients were advised to seek medical counsel. - Funding for the study included support from Moderna; findings were published in Science Translational Medicine and commentators called for further research on genetics, the microbiome, and prior inflammation as potential contributors.
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by Maria Cohut, Ph.D. on October 1, 2026 — Fact checked by Jill Seladi-Schulman, Ph.D. ![Black person standing in waiting room following COVID-19 vaccination](https://media.post.rvohealth.io/wp-content/uploads/sites/3/2026/10/getty_1320037511_header_1296x728-1024x575.jpg)Share on PinterestSubtle differences in immune system reactions may explain why some people get more serious side effects from vaccination. Dimensions/ Getty Images * **Most people who receive a seasonal flu or COVID-19 vaccine experience no or very mild side effects.** * **A recent study suggests that individuals who experience more serious side effects from vaccination do so because of subtle differences in their immune systems, which influence the body’s response to vaccines.** * **The research took COVID-19 mRNA vaccinations as a case study, and looked at both human participants and mouse models.** * **Family physician Clare Thompson, MBBS, further explains what to do if you are concerned about side effects.** A research team from the Center for Vaccinology at the University of Geneva (UNIGE) and Geneva University Hospital (HUG), in Switzerland, recently looked into why some people experience serious side effects post-seasonal vaccination when, in most cases, side effects are mild or even non-existent. The researchers found that the answer may lie in subtle changes to an individual’s immune system, which influence how their body responds to the vaccine. The UNIGE and HUG researchers have published their findings in [Science Translational Medicine](https://www.science.org/doi/10.1126/scitranslmed.aee4776). Some of the funding for the study was granted by the pharmaceutical and biotechnology company Moderna. [Arnaud Didierlaurent](https://www.ige3.unige.ch/research/faculty-members/didierlaurent-arnaud), Ing. PhD, associate professor at the Center for Vaccinology at UNIGE and HUG, and in the Department of Pathology and Immunology at the Faculty of Medicine, UNIGE, senior author of the study, explained in a [press release](https://www.unige.ch/medias/en/2026/vaccination-pourquoi-sommes-nous-inegaux-face-aux-effets-secondaires): > “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.” ## Signaling protein activity influences immune response For this study, the research team recruited 51 healthy adults with a median age of 43.5 years, who received 2 doses of a COVID-19 [mRNA vaccine](https://www.medicalnewstoday.com/articles/mrna-vaccine-vs-traditional-vaccine). The researchers closely monitored participants for 1 week following the administration of each vaccine dose to register any side effects. What they found was that “an interferon-related antiviral defense system [likely explains] differences in side effects between individuals,” said [Natacha Madelon](https://www.unige.ch/medecine/pati/en/groupes/1025didierlaurent/group-members/natacha-madelon), PhD, senior research and teaching assistant at the Center for Vaccinology and first author of the study, in the press release. Cells release interferon, a type of signaling protein, when they sense a virus, as a means of alerting other cells to get ready to fend off the pathogen. Yet not everyone’s bodies have the same ability to release these signaling proteins. **And “the more active a person’s natural interferon response, even before vaccination, the more pronounced their reactions to vaccination are likely to be,” Madelon explained in the press release.** When a person receives a vaccine, their body is essentially learning to respond to and fight the pathogen they are getting vaccinated against. As the body learns, the immune system becomes activated, which explains the cold and flu-like symptoms some people experience after vaccination. ## Stronger reactions to the vaccines can lead to stronger side effects To better understand the differences in immune responses following vaccination, the researchers further experimented with mouse models. They confirmed that, after the first dose of the vaccine, the mice developed [antibodies](https://www.medicalnewstoday.com/articles/what-is-an-antibody), which are disease-fighting proteins and trained T cells, a type of [white blood cells](https://www.medicalnewstoday.com/articles/327446), to recognize these antigens. **Following the administration of the second vaccine dose, the researchers found that this acquired immunity can boost the response of other white blood cells called monocytes very rapidly, which, in turn, can lead to a stronger reaction to the vaccine.** Commenting on the study findings, [Clare Thompson](https://www.cadoganclinic.com/about-us/our-consultants/dr-clare-thompson/), MBBS, a general practitioner at the Cadogan Clinic in London, United Kingdom, who was not involved in this research, told _MNT_ that “this new study suggests that some people are naturally more prone to short-term vaccine reactions because their innate immune system has a more active interferon response.” “Genetics, the microbiome, and previous inflammation may play a role, although more research is needed,” Thompson explained. “It’s important to note that these were generally mild, temporary reactions rather than serious complications,” she added. ### Can individuals take any measures to prevent or mitigate side effects? “There is currently no way to predict or prevent these immune responses,” Thompson told _MNT_. **“Most vaccine side effects settle within a few days, so rest, hydration, and simple measures such as [taking] paracetamol [[acetaminophen](https://www.medicalnewstoday.com/articles/drugs-acetaminophen-oral-forms)], where appropriate, can help manage symptoms,” the doctor advised.** “The study also highlights that experiencing stronger side effects does not mean the vaccine is working better, and having little or no reaction does not mean it is less effective,” she emphasized. ### Is there anyone who should avoid COVID and flu vaccines altogether because of the risk of side effects? “The study does not identify a group who should avoid vaccination,” said Thompson. “Its findings relate mainly to temporary symptoms following mRNA COVID vaccination, and the researchers are still investigating whether the same mechanisms apply to other vaccines, including flu vaccines,” she cautioned. **Thompson advised that, for the time being, the only people who need to seek medical counsel before receiving a seasonal vaccine are those** **concerned about a potential serious allergic reaction to a vaccine ingredient.** Read more about the current vaccine guidelines for seasonal flu, COVID-19, and RSV shots [here](https://www.medicalnewstoday.com/articles/experts-clarify-flu-covid-rsv-vaccine-guidance-what-to-know), and how to cope with vaccine anxiety [here](https://www.medicalnewstoday.com/articles/fainting-and-vaccination-what-to-know-and-what-to-do). * [Flu / Cold / SARS](https://www.medicalnewstoday.com/categories/flu-sars) * [Immune System / Vaccines](https://www.medicalnewstoday.com/categories/immune-system) * [COVID-19](https://www.medicalnewstoday.com/categories/covid-19) * [Flu](https://www.medicalnewstoday.com/categories/flu) ### How we reviewed this article: History Share this article [](https://www.facebook.com/sharer/sharer.php?u=https%3A%2F%2Fwww.medicalnewstoday.com%2Farticles%2Fvaccines-why-some-people-more-likely-experience-side-effects-what-to-do%3Futm_medium%3Dsocial%26utm_source%3Dfacebook%26utm_campaign%3Dsocial-sharebar-referred-desktop "Share on Facebook") [](https://twitter.com/intent/tweet?via=mnt&text=Do%20you%20get%20bad%20side%20effects%20from%20seasonal%20vaccines%3F%20This%20may%20be%20why&url=https%3A%2F%2Fwww.medicalnewstoday.com%2Farticles%2Fvaccines-why-some-people-more-likely-experience-side-effects-what-to-do%3Futm_medium%3Dsocial%26utm_source%3Dx%26utm_campaign%3Dsocial-sharebar-referred-desktop "Share on X") ![](https://i0.wp.com/post.medicalnewstoday.com/wp-content/uploads/sites/3/2020/06/500x500_Maria_Cohut.png?w=105&h=105) Written by Maria Cohut, Ph.D. on October 1, 2026 — Fact checked by Jill Seladi-Schulman, Ph.D. ## Was this article helpful? YesNo ### Read next * [![Thumbnail for article: COVID-19 vaccines: 76% of reported side effects may be due to ‘nocebo’ effect](https://media.post.rvohealth.io/wp-content/uploads/sites/3/2022/01/vaccine_side_effect_nocebo_732x549_thumb-732x549.jpg)](https://www.medicalnewstoday.com/articles/healthy/covid-19-vaccine-76-of-reported-side-effects-may-be-due-to-nocebo-effect/?utm_source=ReadNextRAAS) [COVID-19 vaccines: 76% of reported side effects may be due to ‘nocebo’ effect](https://www.medicalnewstoday.com/articles/healthy/covid-19-vaccine-76-of-reported-side-effects-may-be-due-to-nocebo-effect/?utm_source=ReadNextRAAS) ![Headshot of Robby Berman](https://post.medicalnewstoday.com/wp-content/uploads/sites/3/2021/04/Robby-Potrait-Trimmed-BW.png) Written by: [Robby Berman](https://www.medicalnewstoday.com/authors/robby-berman) [Many of the unpleasant side effects of COVID-19 vaccines are likely due to a nocebo effect, new research suggests.](https://www.medicalnewstoday.com/articles/healthy/covid-19-vaccine-76-of-reported-side-effects-may-be-due-to-nocebo-effect/?utm_source=ReadNextRAAS) * [![Thumbnail for article: Autoimmunity may explain long COVID and rare vaccine side effects](https://media.post.rvohealth.io/wp-content/uploads/sites/3/2021/11/Autoimmunity_Covid_Stocksy_txpcff971fa0bH300_Medium_3689986_Thumb-732x549.jpg)](https://www.medicalnewstoday.com/articles/healthy/autoimmunity-may-explain-long-covid-and-rare-vaccine-side-effects/?utm_source=ReadNextRAAS) [Autoimmunity may explain long COVID and rare vaccine side effects](https://www.medicalnewstoday.com/articles/healthy/autoimmunity-may-explain-long-covid-and-rare-vaccine-side-effects/?utm_source=ReadNextRAAS) [The authors of a recent study ask whether autoimmunity might play a role in long COVID and the very rare side effects seen following COVID-19 vaccines.](https://www.medicalnewstoday.com/articles/healthy/autoimmunity-may-explain-long-covid-and-rare-vaccine-side-effects/?utm_source=ReadNextRAAS) * [![Thumbnail for article: What are the side effects of the Sinopharm COVID-19 vaccine?](https://media.post.rvohealth.io/wp-content/uploads/sites/3/2021/05/Sinopharm-Vaccine-Covid-732x549-Thumbnail-Video-Overlay.jpg)](https://www.medicalnewstoday.com/articles/video-sinopharm-covid-19-vaccine-should-you-worry-about-the-side-effects/?utm_source=ReadNextRAAS) [What are the side effects of the Sinopharm COVID-19 vaccine?](https://www.medicalnewstoday.com/articles/video-sinopharm-covid-19-vaccine-should-you-worry-about-the-side-effects/?utm_source=ReadNextRAAS) [What are the potential side effects of the Sinopharm COVID-19 vaccine? Watch this article to learn more. ](https://www.medicalnewstoday.com/articles/video-sinopharm-covid-19-vaccine-should-you-worry-about-the-side-effects/?utm_source=ReadNextRAAS) * [![Thumbnail for article: Moderna COVID-19 vaccine: What to know about side effects](https://media.post.rvohealth.io/wp-content/uploads/sites/3/2021/04/GettyImages-1231516323_thumb.jpg)](https://www.medicalnewstoday.com/articles/moderna-covid-19-vaccine-what-to-know-about-side-effects/?utm_source=ReadNextRAAS) [Moderna COVID-19 vaccine: What to know about side effects](https://www.medicalnewstoday.com/articles/moderna-covid-19-vaccine-what-to-know-about-side-effects/?utm_source=ReadNextRAAS) [In this feature, we highlight the most common side effects of the Moderna COVID-19 vaccine. We also explore how common they are and other safety considerations.](https://www.medicalnewstoday.com/articles/moderna-covid-19-vaccine-what-to-know-about-side-effects/?utm_source=ReadNextRAAS) * [![Thumbnail for article: Flu vaccination rates improved by text reminders](https://media.post.rvohealth.io/wp-content/uploads/sites/3/2020/02/baby-receiving-a-shot.jpg)](https://www.medicalnewstoday.com/articles/287484/?utm_source=ReadNextRAAS) [Flu vaccination rates improved by text reminders](https://www.medicalnewstoday.com/articles/287484/?utm_source=ReadNextRAAS) [A new study finds that parents who receive text message reminders that their child requires a flu vaccine are significantly more likely to bring their child for vaccination.](https://www.medicalnewstoday.com/articles/287484/?utm_source=ReadNextRAAS) [](https://www.facebook.com/MedicalNewsToday/)[](https://x.com/mnt)[](https://www.pinterest.com/medicalnewstoday/?eq=medical%20news%20today&etslf=4441)[](https://www.instagram.com/medicalnewstoday/)[](https://www.youtube.com/channel/UC7snF15Idi7px6XujWe_h9A)[](https://flipboard.com/@MedNewsToday)
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