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Introduction: Influenza A (H3N2) virus is the major cause of morbidity/mortality due to seasonal influenza over 50 years. Data about the safety/immunogenicity of influenza A/Singapore (H3N2) vaccine are scarce in primary Sjögren syndrome (pSS). Methods: Twenty-one consecutive pSS patients and 42 HC (healthy control individuals) were immunized with influenza A/Singapore/INFIMH-16–0019/2016 (H3N2)-like virus. Rates of SP (seroprotection) and SC (seroconversion), GMT (geometric mean titers), FI-GMT (factor increase in GMT), ESSDAI (EULAR Sjögren's Syndrome Disease Activity Index), and adverse events were appraised before and 4 weeks post-vaccination. Results: pSS and HC had similar mean age (51.2 ± 14.2 vs. 50.6 ± 12.1 years, p = 0.886). Pre-vaccination SP rates were high in pSS and HC (90.5% vs. 71.4%, p = 0.114), and GMT were higher in pSS [80.0 (52.4–160.0) vs. 40.0 (20.0–80.0), p = 0.001]. The percentage of influenza vaccination in the preceding two years was elevated and similar in pSS and HC (94.1% vs. 94.6%, p = 1.000). GMT values augmented in both groups four weeks after vaccination and persisted higher in the first group [160.0 (80.0–320.0) vs. 80.0 (40.0–80.0), p < 0.001] with equivalent FI-GMT [1.4 (1.0–2.8) vs. 1.4 (1.0–2.0), p = 0.410]. Both groups had low and similar SC rates (19.0% vs. 9.5%, p = 0.423). ESSDAI values persisted steadily during the study (p = 0.313). No serious adverse events have occurred. Conclusion: The novel demonstration that the influenza A/Singapore (H3N2) vaccine induces a different pattern of immunogenicity from other influenza A constituents in pSS, featured by a desirable high pre- and post-vaccination immunogenicity, is in line with reported differences in immune responses between strains in trivalent vaccines and may be related to pre-existing immunity. Clinicaltrials.gov: #NCT03540823. Key Points • This prospective study demonstrated a robust pre- and post-vaccination immunogenicity to influenza A/Singapore/INFIMH-16–0019/2016 (H3N2)-like virus in primary Sjögren's syndrome (pSS). • This high immunogenicity pattern may be related to pre-existing immunization, or else it is related to immunogenicity differences of each strain. • This vaccine had an adequate safety profile in pSS, with no impact on disease activity. [ABSTRACT FROM AUTHOR]