Prior treatment with cancer drug likely renders COVID-19 vaccine ineffective, study finds

People who have been treated with rituximab, a widely used cancer drug, or similar drugs respond poorly or not at all to subsequent COVID-19 mRNA vaccines, according to a study by researchers at Stanford Medicine.

In contrast, vaccination immediately prior to such treatments can generate a months-long, durable antibody response, the study found.

Rituximab, marketed under the brand name Rituxan, is widely used alone or in combination with other treatments in people with lymphomas, a type of blood cancer; last year, around 90,000 people were diagnosed with the disease in the United States. The drug targets a molecule called CD-20 found on the surface of immune cells called B cells.

The researchers did not directly assess whether patients treated with rituximab — or with other drugs targeting CD-20 — before being vaccinated subsequently had higher rates of infection with the virus that causes COVID-19. But the findings strongly suggest that people who are newly diagnosed with lymphoma should be offered the vaccine prior to beginning rituximab or similar drugs.

“This finding is likely to be practice-changing,” said Ronald Levy, MD, professor of oncology. “We found that antibody responses to the COVID-19 vaccine were blunted in people who received rituximab up to a year before vaccination. But if they were vaccinated prior to treatment, most responded and were able to hold on to that response during their rituximab treatment.”

Levy is the senior author of the study, which was published Jan. 6 in Blood Cancer Discovery. Oncology instructor Tanaya Shree, MD, PhD, is the lead author.

Measuring antibodies

The researchers measured the vaccination response in 126 lymphoma patients who had been treated with rituximab by assessing the levels of antibodies in their blood to the virus that causes COVID-19. Measuring antibodies in the days and weeks after vaccination is a common method that has been used throughout the pandemic to assess a vaccine’s effectiveness. A strong antibody response to a vaccine is taken to mean the immune system is responding appropriately.