LAUSR

Dear Editor, Psoriasis is a chronic inflammatory disease affecting 1% to 3% of the world's population and results from the interaction between genetics and environmental factors such as stress, infections, and drugs, causing a T-cell-mediated response. Vaccination is an uncommon triggering factor for the flare-ups of several skin diseases, and a potential association between vaccination and the onset or exacerbation of psoriasis has been previously documented. In this letter, we report four new cases of psoriasis flare-ups after an influenza vaccination (Table 1). The first patient was a 41-year-old man with chronic plaque psoriasis undergoing adalimumab therapy who developed a severe flare-up that required hospital admission 24 hours after an intramuscular Chiroflu influenza vaccination (Trivalent A/Victoria/2452/2019 H1N1, A/Hong Kong/2671/2019 H3N2, and B/Victoria/705/2018) (Figure 1). The patient clinically improved after treatment with subcutaneous guselkumab, topical corticosteroids, and emollients. The second patient was a 70-year-old woman with chronic psoriasis who was undergoing treatment with topical corticosteroids and vitamin D analogs. The patient was referred to our department from the emergency room because she had started to develop diffuse erythema and numerous plaques following an intramuscular Chiroflu influenza vaccination 7 days earlier (Figure 2). The patient was started on treatment with oral acitretin, oral prednisone in slow de-escalation, and topical methylprednisolone aceponate, showing marked improvement after 3 weeks. The third patient was a 55-year-old woman with severe chronic psoriasis treated with subcutaneous secukinumab (previously with etanercept, adalimumab, and ustekinumab) who developed a facial psoriasis plaque 24 hours after a subcutaneous Chiroflu influenza vaccination. The patient was treated with topical fluticasone, with complete resolution of the skin lesion in 2 weeks. The fourth patient was a 67-year-old woman with severe chronic psoriasis undergoing guselkumab therapy who developed a guttate psoriasis flare-up following a Chiroflu influenza vaccination 1 month earlier. The patient's biological therapy was changed to brodalumab, with improvement in the cutaneous lesions. New-onset or severe exacerbations of psoriasis following influenza vaccination are uncommon. Most reported vaccination-related psoriasis flare-ups have been classified as guttate and guttate/plaque variants. We report four cases of psoriasis exacerbation following influenza vaccination with H1N1, H3N2, and B influenza strains. In our four patients, the close temporal relationship between the vaccination and the onset of the psoriasis flare-ups suggests a possible causal association. Although the etiological relationship between psoriasis and vaccination remains uncertain, it is known that the influenza vaccine generates T-helper (Th)1 and Th17 immunologic responses, which could represent a possible mechanism for vaccination-induced psoriasis. The immunologic reaction to the influenza vaccination might rely on the generation of interleukin (IL)-6 and IL-22, producing Th17 cells that play a key role in the development of the characteristic epidermal changes of psoriasis. In patients treated with IL-17 inhibitors, Th1 cells might be involved in the development of psoriasis flare-ups instead of Th17 cells. However, we found no differences in the clinical outcomes between the patient treated with secukinumab and the other patients. To date, “psoriasis