Among the eight HCWs who were vaccinated with the BNT162b2 mRNA COVID-19 vaccine, one HCW was diagnosed with RA and was taking MTX. The HCW with RA (patient with RA) was a 60-year-old Japanese male who had been diagnosed with seropositive RA since 2010. The remaining seven HCWs were aged 40-58 years (median 49 years), and there were three females and four males. Details of the characteristics of the participants in this study are presented in Table 1. Obesity and comorbidities were observed in older HCWs. Although age and smoking have been reported as risk factors for lower antibody titers after COVID-19 vaccination, no clear association was observed between antibody titers and age or smoking, possibly owing to the small number of participants (Table 1, Supplementary Table S1).
The patient with RA was in remission after MTX (8 mg/week) and bucillamine (200 mg/day) treatment. MTX was withdrawn for 1 week after each vaccination according to the American College of Rheumatology (ACR) guidance. All participants received a primary vaccination of two doses (30 mug each) in April and May 2021 (3-week interval) and a booster vaccination (single dose, 30 mug) in January 2022. Anti-S antibody titers were measured at 10 days, 7 months, and 8 months (1-month postbooster) after the second vaccination. In the patient with RA and in a poor responder HCW whose anti-S antibody titers at 10 days did not reach the upper detection limit, anti-S antibody titers were also measured at 4 months. The upper detection limit of the anti-S antibody titer was set to 999 U/mL at 10 days and 4 months and 9,999 U/mL afterward.
The anti-S antibody titers of seven HCWs indicated at 10 days were beyond the upper limit of the assay in six (good responders) of seven HCWs and 909 U/mL in one (poor responder) (Figure 1). In the patient with RA, the titer was significantly lower (196 U/mL). At 4 months, the titer of the patient with RA increased to 373 U/mL (1.9-fold increase), which was higher than that of the low-responder HCW (264 U/mL) and similar to the median titer of 380 U/mL in the other HCWs at 7 months (Supplementary Table S1). One-month postbooster, the titer of the patient with RA was 8,437 U/mL, while four HCWs had titers above the upper limit. The titers for the other two HCWs were 6,415 U/mL and 6,817 U/mL, while data were unavailable for one HCW.