New evidence shows that the commonly-prescribed inflammatory bowel disease (IBD) drug infliximab weakens the immune system to COVID-19 infection, potentially increasing the risk of reinfection.

The findings arose from the CLARITY (ImpaCt of bioLogic therApy on saRs-cov-2 Infection and immuniTY) study, which recruited 6,935 patients with Crohn’s disease and ulcerative colitis from 92 UK hospitals between September and December 2020. Researchers plan to follow them up to 40 weeks thereafter.

Two thirds of the cohort (67.6%) took infliximab, while the remainder took vedolizumab. Patients’ median age was 39 years.

The study found that people with COVID-19 infections who also used the inflammatory bowel disease (IBD) drug infliximab had significantly fewer detectable antibodies than those who used vedolizumab, which treats IBD without the immune suppression, according to a study published in the journal Gut.

Lower antibody presence was seen in those who took infliximab, raising the researchers’ concerns about reinfection risk. Researchers note that 3.4% of the infliximab-treated group had SARS-CoV-2 seroprevalence, compared to 6.0% of the vedolizumab-treated group did. Those who were on additional immunomodulators such as thiopurines and methotrexate also had a reduced likelihood of being seropositive.

Of people with confirmed COVID-19 infections, only 48.0% of the 81 treated with infliximab demonstrated seroconversion, compared with 83.3% of the 36 on vedolizumab.

An impaired immune response may boost susceptibility to recurrent COVID-19 and may drive the evolution of new variants of SARS-CoV-2, warn the researchers. However, they are encouraging people to continue to take their medication as the overall COVID-19 risk remains low. Careful monitoring of patients with IBD treated with infliximab, who have been vaccinated against COVD-19, will be needed to ensure they mount a strong enough antibody response to ward off the infection, they advise.

CLARITY study lead, Professor Tariq Ahmad, of the University of Exeter Medical School, said:

“The poor antibody responses observed in patients treated with infliximab raise the possibility that some patients may not develop protective immunity after COVID-19 infection, and might be at increased risk of reinfection. What we don’t yet know is how the use of anti-TNF drugs will impact antibody responses to vaccination.”

The burden of inflammatory bowel disease is rising globally. The incidence of IBD is approximately 0.5-24.5 cases per 100,000 person-years for ulcerative colitis and 0.1-16 cases per 100,000 person-years for Crohn disease. Overall, the prevalence for IBD is 396 cases per 100,000 persons annually.

Around two million people worldwide are prescribed anti-tumour necrosis factor (anti-TNF) drugs, which include infliximab. Anti-TNF drugs are effective treatments for immune-mediated inflammatory diseases, but by suppressing the immune system, they can reduce vaccine effectiveness and increase the risk of serious infection.