Time since rituximab infusion and levels of B-cell reconstitution may be crucial to a humoral response to the mRNA COVID-19 vaccines, two separate small studies suggest.

A study of 89 patients from a rheumatology practice in New York City has shown that among several biological DMARDS and other therapies, only rituximab was associated with a significant risk of the patient having no serological response postvaccination.

Thirty of the patients were on rituximab, making it the largest cohort of patients on the therapy to be assessed for response to COVID-19 vaccines to date, the researchers wrote in a letter to the Annals of the Rheumatic Diseases.

Patients were assessed after almost all had undergone two vaccinations with one of the two mRNA vaccines: either Pfizer/BioNTech (57%) or Moderna (43%).