Should clinicians measure antibodies?
The Food and Drug Administration and the Centers for Disease Control and Prevention have recommended that health care providers and the public not use COVID-19 antibody tests as a way to gauge immunity after exposure to SARS-CoV-2 and after receiving a COVID-19 vaccination. The ACR’s guidance on COVID-19 vaccination for patients with rheumatic and musculoskeletal diseases strongly recommends against ordering antibody tests for patients with autoimmune inflammatory rheumatic diseases as a way to measure immunity.
“Generally, such measurements are not recommended as the clinical correlate of various antibody levels are not known,” Dr. Jyssum said. “With regular infusions of rituximab or other anti-CD20 agents, one cannot expect that these patients will develop significant levels of antibodies.”
However, she said there might be situations where it’s useful to know whether a patient has developed antibodies at all. “Assessing the significance of specific antibody levels is difficult, and the subject of scientific studies. Patients lacking a humoral vaccine response are left to rely on their T-cell responses and on infectious control measures to prevent disease.”
Dr. Spiera said he disagreed with guidelines recommending against checking antibody levels after vaccination, “particularly in patients treated with immunosuppressive medications that might be expected to blunt their serologic response to the vaccines.
“Although we cannot be sure what level of measurable antibodies offer what level of protection, most clinicians would agree that patients who demonstrate no detectable antibodies (which is a common finding in rituximab-treated patients) should be considered at higher risk,” he said. “Indeed, recommendations regarding booster vaccine administration in general was initially based on the observation of declining antibody levels with longer time from vaccination.”
Do COVID-19 vaccine boosters help patients on anti-CD20 therapy?
As of January 2022, the FDA and CDC have recommended a third primary series shot of COVID-19 vaccines for some moderately to severely immunocompromised patients as young as 5 years old (for Comirnaty vaccine) or a booster shot of either Comirnaty or Spikevax for everyone aged 12 years and older, including immunocompromised people, while the ACR goes into more detail and recommends clinicians time a patient’s booster shot with temporary treatment interruption.
In The Lancet Rheumatology, Dr. Jyssum and colleagues recently published results from the prospective Nor-vaC study examining the humoral and cell-mediated immune responses of 87 patients with RA being treated with rituximab who received the Comirnaty, Spikevax, or Vaxzevria (AstraZeneca) COVID-19 vaccines; of these, 49 patients received a booster dose at a median of 70 days after completing their primary series. The results showed 19 patients (28.1%) had a serologic response after their primary series, while 8 of 49 patients (16.3%) who received their booster dose had a serologic response.
All patients who received a third dose in the study had a T-cell response, Dr. Jyssum said. “This is reassuring for patients and clinicians. T cells have been found to be important in countering COVID-19 disease, but whether we can rely on the T-cell response alone in the absence of antibodies to protect patients from infection or from serious COVID disease is still not determined,” she said.
When asked if she would recommend COVID-19 vaccine booster doses for patients on rituximab, Dr. Jyssum replied: “Absolutely.”
Another study, recently published in Annals of the Rheumatic Diseases, examined heterologous and homologous booster doses for 60 patients receiving rituximab without seroconversion after their COVID-19 vaccine primary series. The results showed no significant difference in new seroconversion at 4 weeks based on whether the patient received a vector or mRNA vaccine (22% vs. 32%), but all patients who received a booster dose with a vector vaccine had specific T-cell responses, compared with 81% of patients who received an mRNA vaccine booster. There was a new humoral and/or cellular response in 9 of 11 patients (82%), and most patients with peripheral B cells (12 of 18 patients; 67%) achieved seroconversion.
“Our data show that a cellular and/or humoral immune response can be achieved on a third COVID-19 vaccination in most of the patients who initially developed neither a humoral nor a cellular immune response,” the researchers concluded. “The efficacy data together with the safety data seen in our trial provide a favorable risk/benefit ratio and support the implementation of a third vaccination for nonseroconverted high-risk autoimmune disease patients treated with B-cell–depleting agents.”
Dr. Spiera said booster doses are an important part of the equation, and “it is important to consider factors that would be associated with a greater likelihood of achieving a serologic response, particularly in those patients who did not demonstrate a serologic response to the initial vaccines series.
“Preliminary data shows that the beginnings of B-cell reconstitution is also associated with a positive serologic response following a booster of the COVID-19 vaccine,” he said.
The authors of the cited studies reported numerous relevant financial disclosures. Dr. Spiera and Dr. Jyssum reported no relevant financial disclosures.