Exeter, UK—A study involving inflammatory bowel disease (IBD) patients is calling into question the effectiveness of COVID-19 vaccines in people prescribed antitumor necrosis factor (anti-TNF) drugs.

An online report in the journal Gut discusses how infliximab, commonly prescribed to Crohn’s disease and ulcerative colitis patients, blunts the immune system to COVID-19 infection, potentially increasing the risk of reinfection.

That information comes from the CLARITY study, which recruited 6,935 patients with Crohn’s disease and ulcerative colitis from 92 UK hospitals between September and December 2020. It determined that fewer than half of people with IBD who were treated with infliximab had detectable antibodies after SARS-CoV-2 infection, the coronavirus that causes COVID-19.

Authors of that study warn that an impaired immune response might boost susceptibility to recurrent COVID-19 and even help drive the evolution of new variants of SARS-CoV-2, the virus responsible for the infection.

Still, they are encouraging people to continue to take their anti-TNF medications because overall COVID-19 risk remains very low.

Researchers also strongly advise close monitoring of IBD patients treated with infliximab who have been vaccinated against COVID-19. The concern is their ability to mount a strong enough antibody response to be protective against infection, even after immunization, to ward off the infection, they advise. The CLARITY study lead, Professor Tariq Ahmad, DPhil, 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 use of anti-TNF drugs will impact antibody responses to vaccination.”

Dr. Ahmad said the study “will continue to follow participants for 40 weeks to investigate important questions regarding the impact of immunosuppressive drugs on immunity to SARS-CoV-2 infection and COVID-19. Modified vaccine schedules may be required if impaired antibody responses are also observed following vaccination. However, because the overall risk of COVID-19 is low in this patient group, we would still strongly encourage patients to continue to take anti-TNF medicines.”

Background information in the study advises that about 2 million patients worldwide are prescribed anti-TNF drugs, which include infliximab, and are effective treatments for immune-mediated inflammatory diseases. The downside in the current pandemic, however, is that the drugs also suppress the immune system, thereby reducing vaccine effectiveness and increasing risk of serious infection.

For the CLARITY study researchers compared antibody responses to SARS-CoV-2 in patients treated with infliximab to an alternative medication, vedolizumab, that blocks inflammatory cells entering the gut without reducing immune responses to infections or vaccinations. They recruited 6,935 IBD patients, average age 39 years, from 92 UK hospitals between September and December 2020. About two-thirds of them were being treated with infliximab, with the remaining on vedolizumab.

About 8% of the infliximab group and 9% of the vedolizumab group had symptoms indicative of COVID-19 infection, and 89 of those taking infliximab and 38 of those taking vedolizumab tested positive for the virus.

Results indicate that, while rates of COVID-19 infection and hospitalizations were similar between infliximab- and vedolizumab-treated patients, infliximab-treated patients who recovered were much less likely to have a positive antibody test—3.4% for infliximab versus 6% for vedolizumab.

Only about half, 48%, of patients treated with infliximab whose COVID-19 infection was confirmed by a swab test subsequently developed antibodies compared with 83% of those treated with vedolizumab, according to researchers.

The authors suggest the findings couldn’t be explained by differences in acquisition or severity of infection alone, but that infliximab appears to be directly influencing antibody responses to infection. Supporting that supposition was that rates of positive antibody tests were lowest in participants who were also taking other drugs that suppress the immune system, such as azathioprine, mercaptopurine, or methotrexate.

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