Background As COVID-19 became a pandemic, the urgent need to find an effective treatment vaccine has been a major objective. Vaccines contain adjuvants which are not exempt from adverse effects and can trigger the autoimmune/inflammatory syndrome induced by adjuvants (ASIA). There is very little information about autoimmune endocrine disease and the ASIA after the use of mRNA-based SARS-CoV2 vaccination. Case series We report three cases and also review the literature showing that the thyroid gland can be involved in the ASIA induced by the mRNA-based SARS-CoV2 vaccination. We present the first case to date of silent thyroiditis described in the context of SARS-CoV2 vaccination with Pfizer/BioNTech. Also, we discuss the first subacute thyroiditis in the context of SARS-CoV2 vaccination with the Moderna's vaccine. Finally, we provide another case to be added to existing evidence on Graves' disease occurring post-vaccination with the Pfizer/BioNTech vaccine. Discussion Adjuvants play an important role in vaccines. Their ability to increase the immunogenicity of the active ingredient is necessary to achieve the desired immune response. Both the Moderna and the Pfizer/BioNTech vaccines use mRNA coding for the SARS-CoV2 S protein enhanced by adjuvants. In addition, the cross-reactivity between SARS-CoV2 and thyroid antigens has been reported. This would explain, at least, some of the autoimmune/inflammatory reactions produced during and after SARS-CoV2 infection and vaccination. Conclusion The autoimmune/inflammatory syndrome induced by adjuvants involving the thyroid could be an adverse effect of SARS-CoV2 vaccination and could be underdiagnosed.