Multiple sclerosis patients treated with Rituximab have better responses to the COVID-19 vaccine if they have higher B cell counts. In patients with B cell counts of 40 microliters or more, nine of 10 patients developed protective levels of antibodies, while significantly fewer with lower counts had similar responses.

Researchers at Uppsala University and Uppsala University Hospital in Uppsala, Sweden, have studied how MS patients treated with Rituximab react to vaccination against COVID-19. The purpose was to determine the optimal level of B cells for the patient to form sufficient numbers of antibodies after vaccination.

Blood from a total of 67 individuals with MS was analyzed, of whom 60 were undergoing treatment with Rituximab and 7 were going to begin treatment after their COVID-19 vaccinations. Blood samples were taken before and after vaccination to study the levels of B cells and antibodies for SARS-CoV-2. The patients received two doses of Pfizer’s COVID-19 vaccine, Comirnaty, with the active substance tozinameran.

The results show the levels of B cells varied greatly among the subjects. The longer a patient had been treated with Rituximab, the longer it took their B cells to recover. For some patients, it took more than a year before the B cells began to come back.

The patients who responded best to the vaccine and formed sufficiently high levels of antibodies had on average 51 B cells per microliter before the vaccination. For the group that did not reach sufficient levels, the average was 22 B cells per microliter.

Researchers found there was a threshold with a level of B cells at 40 per microliter or more where 90 percent formed protective levels of antibodies. Of the patients who were undergoing MS treatment with Rituximab, 72 percent formed sufficiently high levels of antibodies. The best effect with the highest percentage of antibodies was found in subjects who had never been treated with Rituximab.

The researchers have also studied the ability of T cells to react to the virus. No differences were found between subjects who had been treated with Rituximab and those who had never been treated.

The ability of the T cells to react to the virus was just as strong in those who had received treatment. The levels of B cells before vaccination also did not affect the T-cell response, which suggests all patients have a certain benefit from the vaccination, even if antibodies are not formed.

The findings were published in the journal JAMA Network Open.