Background: Adult-onset Still's disease (AOSD) is an autoinflammatory multi-systemic syndrome. Macrophage activation syndrome (MAS) is a potentially life-threatening complication of AOSD with a mortality rate of 10-20%. Especially viral infection is thought to be a common trigger for development of MAS. On the other hand, the occurrence of MAS following vaccinations is extremely rare and has been described in a few cases after measles or influenza vaccinations and more recently after ChAdOx1 nCoV-19 (COVID-19 viral vector vaccine, Oxford-AZ).
Case presentation: We report the case of a twenty-year-old female with adult-onset Still's disease (AOSD), who developed a MAS six days after receiving her first COVID-19 vaccine dose of BNT162b2 (mRNA vaccine, BioNTech/Pfizer) with ferritin levels of 136,680 mu g/l (ref.: 13-150 mu g/l).
Conclusions: To the best of our knowledge, this is the first case report of development of MAS in a patient with preexisting AOSD after vaccination in general, and SARS-CoV-2 vaccination in particular. The new mRNA vaccines have generally shown a reassuring safety profile, but it has been shown that nucleic acids in general, including mRNA can act as pathogen-associated molecular patterns that activate toll-like receptors with extensive production of pro-inflammatory cytokines and further activation of immune cells. Proving an interferon 1 response in our patient directly after vaccination, we think that in this particular case the vaccination might have acted as trigger for the development of MAS. Even if it remains difficult to establish causality in the case of rare adverse events, especially in patients with autoimmune or autoinflammatory conditions, these complications are important to monitor and register, but do not at all diminish the overwhelming positive benefit-risk ratio of licensed COVID-19 vaccines.