# Gut bacteria plays a huge role in vaccine side effects

Source: [Earth.com](https://www.earth.com/science/gut-bacteria-plays-a-huge-role-in-vaccine-side-effects/) · 2026-11-12 · Earth & Climate
Page: https://themorning.science/story/gut-bacteria-plays-a-huge-role-in-vaccine-side-effects-4bd8be1d476c8de6
Kind: research · Impact: low

## In brief

- Some people get noticeable side effects such as chills and headaches after a COVID-19 shot, while others barely notice any, and this split holds across doses.
- Researchers have found that part of the reason lies in gut bacteria, which were already present before the vaccine was given.
- The reporting is based on a single Earth.com article; the study's details are not given in the provided source.

## Why it matters

It offers a biological explanation for why people differ in vaccine reactions, which could inform future work on predicting or managing side effects.

## Coverage

- [Gut bacteria plays a huge role in vaccine side effects](https://www.earth.com/science/gut-bacteria-plays-a-huge-role-in-vaccine-side-effects/) — Earth.com, 2026-11-12

Tags: vaccines, gut microbiome, side effects, immunology, covid-19

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Brief generated by AI (claude-haiku-5-5) from the reporting listed under Coverage. Headlines belong to their publishers. The Morning Science – https://themorning.science