Before the immunological Big Bang.

The gut microbiome before vaccination is linked to subsequent inflammatory reactions and fever.

• Why it matters: Understanding this relationship matters because the initial microbiome may affect vaccine responses and adverse effects, yet this period remains poorly characterized.
• What they did: The study examined the gut microbiome prior to vaccination and its association with later inflammatory outcomes, focusing on how pre-vaccination microbiome composition influences immune reactions.
• The result: Findings suggest that the microbiome before vaccination may predict inflammatory responses and fever, potentially enabling targeted interventions to improve vaccine safety and efficacy.