Discussion
SARS-CoV-2 infection, B cell malignancies [, malignant lymphoma, aggressive non-Hodgkin lymphoma, mature T/NK-cell neoplasms, NHL
MALIGNANT LYMPHOMA, HEMATOLOGICAL MALIGNANCIES, SARS-COV-2 INFECTION, NHL
In our institution, we routinely recommend COVID-19 vaccination to our patients, especially these with malignant lymphoma who were receiving active treatment. Recent studies have shown that the seroconversion rates after two doses of mRNA-based COVID-19 vaccines were 34–58% in patients with aggressive non-Hodgkin lymphoma (NHL) and 43–61% in patients with indolent NHL [ This study was conducted in patients with mature T/NK-cell neoplasms, and although none of the patients had received anti-CD20 monoclonal antibodies at the time of vaccinations, the seroconversion rate and median antibody titer after two doses were lower than those in HC, as previously reported for patients with B cell malignancies [In patients with mature T/NK-cell neoplasms, the seroconversion rate after the second dose was 73.7%, which was significantly lower than that in HC, but the seroconversion rate after the booster dose in the patients was 100%, which was the same as that in HC. In patients with hematological malignancies, although no significant association was found between the seroconversion rate after vaccination and the incidence of COVID-19, no patient with seroconversion died from COVID-19 [The median antibody titer in patients aged 75 years or older was significantly lower than that in patients younger than 75 years of age at 3 months after the primary vaccination. However, the median antibody titer after administration of the booster vaccine in patients aged 75 years or older increased to a level comparable to that in patients younger than 75 years of age. Although the preventive antibody titer against SARS-CoV-2 infection is unknown, it has been reported that higher antibody titers contributed to protection against SARS-CoV-2 infection [Our study has several limitations. HC were health care workers. Although our hospital had not accepted COVID-19 patients, the possibility of individuals with asymptomatic COVID-19 cannot be ruled out. The median age of the patient was 74 (range: 43–87) years, whereas the median age of HC was 55 (50–72) years. Thus, there appeared to be differences in the age distribution of patients and HC. This study included a heterogenous patient population and only humoral immunity was evaluated. T cell immunity, which is also important for preventing a severe course of COVID-19, was not evaluated [In conclusion, in patients with mature T/NK-cell neoplasms, both the seroconversion rate and antibody titer after the second vaccination were significantly lower than those in HC. In contrast, in patients who received the booster dose, the median antibody titer was significantly lower than that in HC who received the booster dose, but the seroconversion rate increased to 100% in the patients after the booster. Of note, the booster vaccine resulted in a significant increase of antibodies in elderly patients who had shown a response that was inferior to that in younger patients after two doses of vaccination. Therefore, vaccination more than three times may have the advantage for patients with mature T/NK-cell neoplasms, especially in elderly patients.