2021;174:1334\1336. 26 (61.9%) patients, respectively. Ratios of pre\ and postvaccination antibody titers were 53, 40, and 174 in the unchanged, relief, and worsened groups, respectively. The worsened group had the significantly highest antibody titer ratio (Value[%])0.45Fisher’s exactMale12?(46.2)3?(42.9)2 (22.2)Complication of pneumoniae ([%])0.72Fisher’s exactNo14?(56.0)3?(42.9)3?(33.3)+6?(24.0)3?(42.9)4?(44.4)No examination5?(20.0)1?(14.3)2?(22.2)Past history ([%])?0.08Fisher’s exact+16?(61.5)5?(71.4)9?(100.0)Working situation ([%])0.83Fisher’s exactContinued16?(62)4?(57)4?(44)Changed work type and continued3?(12)?1?(14)3?(33)Temporary leave from work6?(23)2?(29)2?(22)Resignation1?(4)0?(0)0?(0)Smoking history ([%])0.26Fisher’s exactNever16?(62)5?(71)7?(78)Quit smoking8?(31)0?(0)1?(11)Current smoker2?(8)2?(29)1?(11)Symptom ([%])Fatigue15?(55.6)5?(18.5)4?(14.8)Joint pain2?(7.4)0?(0)2?(7.4)Taste and olfactory abnormality5?(18.5)0?(0)0?(0)Numbness0?(0)0?(0)1?(3.7)Sore throat0?(0)0?(0)1?(3.7)Dizziness0?(0)1?(3.7)0?(0)Memory impairment1?(3.7)?0?(0)0?(0)Palpitations0?(0)1?(3.7)0?(0)Cough1?(3.7)0?(0)0?(0)Headache0?(0)0?(0)1?(3.7)Chest ache1?(3.7)0?(0)0?(0)Anxiety1?(3.7)0 (0)0?(0)Onset\before vaccination (days)196?(110C238)146?(58C338)173?(136C227)0.84KruskalCWallisBlood sampling date before vaccination\vaccination date (days)44?(24C77)30?(19C39)36?(35C94)0.25KruskalCWallisVaccination date\postvaccination blood sampling (day)15?(14C17)24?(14C40)15?(13C17)0.21KruskalCWallisBefore vaccination SIgG (AU/ml)456 (217C918)773?(163C930)360?(219C807)0.94KruskalCWallisAfter the first vaccination SIgG (AU/ml)25?717?(13?171C36?824)21?787?(14?846C30?910)38?186?(30?979C71?458)Ratio of antibody titer53?(29C94)40?(18C110)174?(115C198)0.06KruskalCWallis Open in a separate window Abbreviations:?IgG,?immunoglobulin G; RBD,?receptor\binding domain. Open in a separate window Figure 1 This figure shows the among\three group (unchanged, relief, and worsened) comparisons of antibody titers before and after vaccination. The ratios of pre\ and postvaccination antibody titers show no significant differences (KruskalCWallis test; p?=?0.06). The worsened group shows a significantly higher antibody titer ratio than the non\worsened group (MannCWhitney test; p?=?0.02). SIgG, anti\spike RBD IgG The ratios of pre\ and postvaccination antibody titers were 53, 40, and 174 in the unchanged, relief, and worsened groups, respectively, without significant among\group differences (KruskalCWallis test; p?=?0.06). However, the worsened group showed a significantly higher antibody titer ratio than the non\worsened group (MannCWhitney test; p?=?0.02). There were 12 (29%) patients who did not receive the second vaccination. 4.?DISCUSSION This study showed no postvaccination changes in the SJB2-043 symptoms of Long COVID; moreover, the symptom relief rate was lower than that reported in a previous study. 8 Furthermore, the worsened group showed a significantly higher change ratio in the antibody titer than SJB2-043 the nonworsened group. In most patients, prevaccination antibody titers are equal or less than those after a single vaccination in uninfected persons. 15 Lack of vaccination increases the risk of reinfection even in patients with previous SARS\CoV\2 infection. 11 Therefore, vaccination is necessary for preventing reinfection in patients with Long COVID. However, in our study, 29% of patients did not undergo the second vaccination. Patients refused to undergo the second vaccination because of worsening Long COVID symptoms, concerns about strong side effects, and satisfaction with the antibody titers after the first vaccination. Regarding antibody titers, studies have reported that sufficient antibody titers can be obtained by a single vaccination for patients with previous SARS\CoV\2 infection. 15 , 16 Our findings showed that even in patients with Long COVID, a sufficient antibody titer can be obtained with a single vaccination. A small\scale study in real\world settings reported no significant difference in the occurrence of reinfection between infected individuals with only one vaccination and without vaccination. 11 Therefore, future studies are warranted. The third vaccination program has started; however, there is a need to address worries regarding additional vaccinations among patients with Long COVID. The higher increased rate of the antibody titer in the worsened group than in the nonworsened group suggests that an excessive immune response to vaccination may be associated with worsening of sequelae. Numerous autoantibodies are produced after COVID\19 infection and cause various symptoms 17 ; moreover, immune disorders are associated with the pathophysiology of sequelae. 18 In case an immune overreaction to vaccination worsens the sequelae, the sequelae may result from an immune disorder. Gracia\Abelln FACD et al. 19 reported a relationship between low antibody titers and sequelae. Antibodies are involved in the regulation of inflammatory responses through activation of Fc\ receptors, Toll\like receptors, and complements, which induce the secretion or suppression of various proinflammatory SJB2-043 and anti\inflammatory mediators. Therefore, they suggested that low peak antibody titers worsened sequelae symptoms. However, the previous findings cannot be directly compared with our findings. The previous study included admitted patients; contrastingly, most of our patients were in the mild acute phase. Vaccination of patients with Long COVID can be recommended without changes in sequelae, psychiatric symptoms, or quality of life. 20 Unvaccinated patients with Long COVID should be vaccinated to prevent reinfection. However, if the sequelae symptoms worsen after the first vaccination, the second or third vaccination should not be coercively administered. This study has several limitations. First, this was a single\center study with a small sample size. Changes in sequelae symptoms.