People who take a commonly-prescribed drug for inflammatory bowel disease (IBD) should not assume they are protected after a first dose of vaccine.

This is the finding of new research, from a number of institutions including Imperial College London. The study measured antibody responses after vaccination with the Pfizer/BioNTech or the Oxford/AstraZeneca COVID-19 vaccine in 865 people treated with infliximab, an anti-tumour necrosis factor (anti-TNF) biologic drug, prescribed to around two million people worldwide.

The study emphasizes the importance of a second vaccine dose, which I am encouraging all of my patients to do Dr Nick Powell Study author

Anti-TNF drugs are effective treatments for immune-mediated inflammatory diseases, but by suppressing the immune system, they can reduce vaccine effectiveness and increase risk of serious infection.

The research, published in the journal GUT, is an output from the CLARITY Study , which is funded by the NIHR and Crohn’s and Colitis UK.

The research found that people treated with infliximab had significantly lower concentrations of antibodies, when compared to 428 people on an alternative treatment, vedolizumab.

Vaccines work by stimulating the immune system to produce antibodies that protect individuals from any future infection. For a vaccine to be effective, it needs to trigger a sufficient number of virus-targeting antibodies to prevent any subsequent infection.

Protection against COVID-19

After a single dose of vaccine, only about one third of participants (103 of 328) treated exclusively with infliximab generated adequate levels of antibodies to the virus for the vaccine to be considered effective.

In participants simultaneously taking infliximab and immunomodulator drugs, such as azathioprine or methotrexate, the levels of antibodies were even lower after a single vaccine dose; only 125 of 537 met the threshold of a positive antibody test.

However, in a sub-group of people who had previously been infected with COVID-19, and also in the few patients studied who had already had a second dose of vaccine, the vaccine-triggered antibody responses rose significantly, indicating an effective response after two exposures. Based on these observations, the researchers conclude that people taking anti-TNF drugs should be considered a priority for a second vaccination.

The  CLARITY study recruited 6,935 patients with Crohn’s disease and ulcerative colitis from 92 UK hospitals between September and December 2020, to investigate the impact of these drugs on COVID-19 susceptibility and protective immunity that follows infection or vaccination. Previously, the study found that infliximab blunts the immune system to COVID-19 infection, potentially increasing the risk of reinfection.

Second dose needed

Dr Nick Powell, co-senior author of the study from Imperial's Department of Metabolism, Digestion and Reproduction, said: "This is a really important study, showing that a single dose of SARS-CoV2 vaccine is insufficient to generate protective antibody responses in patients treated with anti-TNF

Poor antibody responses to a single dose of vaccine exposes these patients to a potential increased risk of COVID-19 Dr Tariq Ahmad Study author

drugs. This is important because millions of people around the world take these drugs. Reassuringly, in patients who had been given a second dose of vaccine, most of them mounted excellent responses. The study emphasizes the importance of a second vaccine dose, which I am encouraging all of my patients to do."

CLARITY study lead Dr Tariq Ahmad, from the University of Exeter, added: “Poor antibody responses to a single dose of vaccine exposes these patients to a potential increased risk of COVID-19. However, we found much higher antibody levels in people vaccinated after a previous COVID-19 infection and in the small number of patients who had received two vaccine doses suggesting that all patients receiving these drugs should be prioritised for optimally timed second doses.”

500,000 people across the UK live with Inflammatory bowel disease (IBD) of which ulcerative colitis and Crohn’s disease, are the two main forms. Symptoms include urgent and frequent bloody diarrhoea, weight loss, pain, and extreme fatigue.

At the start of the COVID-19 pandemic the UK Government advised that patients taking anti-TNF medicines could be at increased risk of complications from coronavirus. All were advised to follow strict social distancing measures, and some, depending on the severity of their condition, were advised to shield.

This is the first robust evidence that people with Crohn’s and Colitis do not develop the expected antibodies after their first vaccination dose Sarah Sleet Chief Executive of Crohn’s & Colitis UK

In the study, a small sub-set of patients showed no antibody response even after two exposures to COVID-19.

Co-author Dr James Goodhand, of the University of Exeter, said: “Our findings come as countries across Europe are opting to delay the second dose of vaccine.

We recommend prioritizing second doses to patients taking anti-TNF drugs, who will remain at high risk after their first dose.

Further data are needed to investigate whether we should be testing antibody concentrations after two doses to identify the small number of patients who have not responded well to vaccination.”

First evidence of poor vaccine response

The study also found evidence that antibody responses were lower in current smokers and participants aged 60 or older, but higher in non-white participants. These findings warrant further investigation in larger studies before firm conclusions can be drawn.

Sarah Sleet, Chief Executive of Crohn’s & Colitis UK, said: “This is the first robust evidence that people with Crohn’s and Colitis - who may need to take specific drugs to suppress their immune system -  do not develop the expected antibodies after their first vaccination dose, although a second dose does improve antibody levels. With 1 in 5 not developing antibodies even after 2 doses, these people will be desperately worried that they remain at risk of catching COVID–19 and may develop a more serious illness at a time when shielding has ended. We need urgent research on the optimal time between the first and second jabs, and the need to be prioritised for any booster jab this Autumn.”

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'Infliximab is associated with attenuated immunogenicity to BNT162b2 and ChAdOx1 nCoV-19 SARS-CoV-2 vaccines in patients with IBD' is published in the journal Gut

Adapted from a press release from the University of Exeter