IBD patients treated with infliximab have poor serological responses to a single dose of a SARS-CoV-2 vaccine, and should only be considered protected after two doses, UK researchers say.
In a study of immunogenicity responses to Pfizer and AstraZeneca vaccines, investigators examined antibody responses and seroconversion rates in 865 infliximab-treated patients.
Their findings, published in the journal Gut, showed that seroconversion rates were 36.1% following a primary Pfizer (BNT162b2) vaccine dose and 27.6% after AstraZeneca (ChAdOx1 nCoV-19) vaccines in patients taking infliximab. Rates were even lower in patients who were also taking immunomodulators ( 27.1% and 20.1% respectively).
Rates of seroconversion were higher in patients treated with vedolizumab monotherapy (74.7% for Pfizer vaccine primary dose, 57.3% for the AstraZeneca vaccine).
Anti-SARS-CoV-2 antibody concentrations were lower in infliximab-treated patients than a control group of 428 patients treated with vedolizumab. Antibody responses to SARS-CoV-2 vaccines were particularly attenuated in older people, in smokers and more likely in those with Crohn’s disease compared to those with ulcerative colitis.
Reassuringly, however, a second dose of vaccine led to seroconversion in most (85%) of the patients, the study investigators noted.
They said the impaired responses to vaccine with infliximab could be expected given the role of TNF in host immune responses, including T-cell dependent antibody production.
“For patients treated with anti- TNF therapy, particularly for those also treated with an immunomodulator, poor antibody responses to a single dose of vaccine exposes them to a potential increased risk of SARS-CoV-2 infection,” they concluded.
“Until patients receive a second vaccine dose, they should consider that they are not protected from SARS-CoV-2 infection and continue to practice enhanced physical distancing and shielding if appropriate,” they advised.
However they also noted that a small subset of patients failed to mount an antibody response even after two antigen exposures.
“Antibody testing and adapted vaccine schedules should be considered to protect these at-risk patients,” they suggested.