Twenty-four JSLE patients and 29 healthy controls were included in the study. Both groups were comparable regarding median current age [14.5 (10.1–18.3) vs. 14 (9–18.4) years, p = 0.448] and female sex [21 (87.5%) vs. 19 (65.5%), p = 0.108]. Frequencies of Caucasian race [14 (58.3%) vs. 17 (58.6%), p = 1.000] and median body mass index (BMI) were similar among these studied groups [21.6 (14.8–31.8) vs. 19.8 (15.2–33.2) Kg/m2, p = 0.318]. JSLE patients and healthy controls had also comparable frequencies of comorbidities: arterial hypertension [1 (4%) vs. 0 (0%), p = 0.453], diabetes mellitus [0 (0%) vs. 0 (0%), p = 1.000], dyslipidemia [0 (0%) vs. 0 (0%), p = 1.000], coronary artery disease [0 (0%) vs. 0 (0%), p = 1.000], hypothyroidism [0 (0%) vs. 0 (0%), p = 1.000], and peptic disease [1 (4%) vs. 1 (3%), p = 1.000]. At study entry, 24 (100%) of JSLE were under hydroxychloroquine, 15 (62.5%) prednisone [median dose of 15 (2.5–30) mg/day] and 20 (83%) were currently treated with immunosuppressive drug, including 12 (50%) mycophenolate mofetil, 5 (21%) azathioprine and 4 (17%) methotrexate.

Before immunization SP rates were comparable in JSLE patients and healthy controls [22 (91.7%) vs. 25 (86.2%), p = 0.678], as well as GMT [102.3 (95%CI 75.0–139.4) vs. 109.6 (95%CI 68.2–176.2), p = 0.231] (Table 1).

At D30, immune response parameters maintained comparable in JSLE and healthy controls including SP [24 (100%) vs. 28 (96.6%), p = 1.000)], SC rates [4 (16.7%) vs. 9 (31.0%), p = 0.338), GMT [162.3 (132.9–198.3) vs. 208.1 (150.5–287.8), p = 0.143], and factor increase in GMT [1.6 (1.2–2.1) vs. 1.9 (1.4–2.5), p = 0.574] (Table 1). A significant increment in GMT was observed from D0 to D30 in JSLE patients (p < 0.001) as well as in the control group (p < 0.001).

The comparison of responders (n = 4) and non-responders (n = 20) JSLE patients based on the SC demonstrated similar current age [14.5 (13–18) vs. 14.6 (10.1–18.3), p = 0.892], female sex [3 (75%) vs. 18 (90%), p = 0.437], Caucasian race [1 (25%) vs. 13 (65%), p = 0.272], baseline SLEDAI [2 (2–4) vs. 2 (0–17), p = 0.846], prednisone use [3 (75%) vs. 12 (60%), p = 1.0], prednisone dose [12.5 (10–15) vs. 15 (2.5–30), p = 0.746] and immunosuppressive drugs, including mycophenolate mofetil [1 (25%) vs. 11 (55%), p = 0.590], azathioprine [1 (25%) vs. 4 (20%), p = 1.0] and methotrexate [1 (25%) vs. 3 (15%), p = 0.544].

Further analysis of possible factors influencing vaccine immune response among JSLE patients demonstrated similar GMT of anti-H3N2 antibodies between patients with SLEDAI < 4 compared to SLEDAI ≥ 4 [167.1 (95%CI 130—214.8) vs. 153.2 (100.4–233.7), p = 0.713], as well as between patients with and without current use of prednisone [171.5 (130.5–225.4) vs. 148.1 (104.7–209.5), p = 0.420], azathioprine [160.0 (64.2–398.6) vs. 162.9 (133.9–198.4), p = 1.0], mycophenolate mofetil [184.9 (145.6–234.7) vs. 142.5 (101.2–200.8), p = 0.185] and methotrexate [113.1 (59.9–213.9) vs. 174.5 (140.6–216.6), p = 0.095].

Disease activity in JSLE measured by SLEDAI-2K score remained stable before and after immunization [2 (0–17) vs. 2 (0–17), p = 0.765] (Table 2). Importantly, no significant changes were observed in the frequencies of positive anti-dsDNA [9 (38) vs. 9 (38), p = 0.480] and hypocomplementemia [4 (17) vs. 3 (13), p = 1.000] among groups (Table 2).

During the study, no significant changes were identified in the median leukocytes [5.09 (1.39–13.7) vs. 4.9 (1.76–11.11) × 103, p = 0.989] as well as lymphocytes [1.52 (0.17–3.15) vs. 1.5 (0.65–2.78) × 103, p = 0.648] (Table 2). Importantly, no significant changes were observed in the frequencies of leukopenia and lymphopenia (Table 2).

The comparison of therapy between entry and at the end of the study revealed no significant changes in most of the JSLE patients (Table 2). In fact, all were receiving antimalarials [24 (100%) vs. 24 (100%), p = 1.000], oral prednisone [15 (62.5%) vs. 15 (62.5%), p = 1.000] with a median dosage of 15 (2.5–30) mg/day during the period, mycophenolate mofetil [12 (50%) vs. 12 (50%), p = 1.000], and methotrexate [4 (17%) vs. 4(17%), p = 1.000] with a median dosage of 17.5 (7.5–25) mg/week during all the study (Table 2). Only one patient started azathioprine [5 (21%) vs. 6 (25%), p = 1.000] but this increase was not significant. Importantly, none of the JSLE patients were taking IVCYC or Rituximab during the period of the study (Table 2).

No serious AE were reported in both groups. Most of the JSLE patients and healthy controls were asymptomatic (58.3% vs. 44.8, p = 0.958) (Table 3). Local and systemic AE were alike in JSLE and healthy controls groups. Local pain (29% and 28%) and headache (25% and 17%) were the most frequent observed AE but their frequencies were alike in both studied groups (Table 3). The apparent higher frequency of coryza in healthy controls [5 (17%) vs. 0 (0), p = 0.056] did not reach statistical significance (Table 3).