<p>Maternal immunisation allows the transfer of protective antibodies to the offspring, reducing the risk of severe infection during early life. While vaccination during pregnancy is clinically recommended, its long-term impact on neurodevelopment remains under investigation. Autism spectrum disorder (ASD) is a neurodevelopmental condition characterised by social and behavioural alterations. Here, we evaluated whether prenatal exposure to the COVID-19 mRNA BNT162b2 vaccine or influenza vaccine affects general and autism-related behavioural outcomes in juvenile (4 weeks) and adult (8 weeks) mouse offspring. We also assessed maternal and fetal immune responses by measuring cytokines, soluble P2X7 receptor, BDNF, CRP, and lipid peroxidation in maternal plasma and fetal brain tissue. Prenatal COVID-19 vaccination elicited a moderate maternal cytokine response (increased IL-6 and KC) without overt fetal brain inflammation. Mild, age- and sex-dependent behavioural changes were observed, including anxiety-related parameters in the elevated plus maze and altered locomotion in the open field at 4–8 weeks, however, no consistent or robust ASD-like behavioural phenotype emerged across ages. Fetal P2X7 receptor levels were elevated, while fetal CRP, BDNF, and TBARS remained unchanged. In adult offspring, BDNF was selectively reduced in the prefrontal cortex, whereas hippocampal BDNF and P2X7 receptor levels in both regions were unaffected. Although embryonic P2X7 receptor levels were transiently elevated following COVID-19 vaccination, these changes were not accompanied by fetal inflammation or persistent adult purinergic alterations. Prenatal influenza vaccination induced mild, age-dependent behavioural alterations, such as increased circling in juveniles and reduced sociability in females, without detectable maternal or fetal inflammatory responses or changes in fetal neurotrophic markers. In contrast, maternal poly(I:C) administration provoked robust systemic inflammation and pronounced fetal brain effects, including elevated cytokines, CRP, P2X7 receptor, and region-specific microglial density, accompanied by persistent reductions in adult BDNF expression. Overall, within the limits of this experimental design, prenatal COVID-19 vaccination did not produce long-lasting ASD-like phenotypes or widespread neurodevelopmental alterations, while influenza vaccination had limited and transient effects. These findings are consistent with the absence of widespread or persistent neurodevelopmental disruption in this experimental model, although further studies—including multiple doses, gestational timepoints, and cellular-level analyses—are warranted to fully elucidate mechanisms and long-term outcomes.</p>