A total of 392 patients were included, the baseline characteristics are summarized in Table 1 and those related to their IBD in Table 2. 8 patients were previously excluded because they had already received a dose of COVID-19 vaccine.
The average age of the patients included at the time of analysis was 49.23 years (SD: 15.4). Regarding the treatments followed by patients at the time of the start of the pandemic (March 2020): monotherapy with biologics was the most frequent (105 patients, 26.99%); followed by patients with combined treatment (biologic + immunosuppressant) (60 patients, 15.42%) and immunosuppressants in monotherapy (57 patients, 14.65%). 43% of patients were not under treatment with any of the above drugs. Regarding the type of biologic used by patients, 43% (62 patients) were on Infliximab, 21% (30 patients) on Adalimumab, 15% (22 patients) on Vedolizumab and 13.2% (19 patients) on Ustekinumab.
At the time of analysis (July 2021), the percentage of patients on biologics had increased compared to the beginning of the pandemic, with therapy that was alone or in combination with immunosuppressants (201 patients, 52%), while those on immunomodulatory therapy alone decreased to 12.1% (47 patients). Finally, 9 patients (2.3%) were on corticosteroid treatment. The distribution in terms of the use of the different biological drugs did not differ significantly from that shown for March 2020.
With respect to the serology extracted to assess the seroprevalence of IgG antibodies against SARS-CoV-2 in patients with IBD, 286 patients (73.15%) were negative, 69 patients (17.65%) were positive and in 36 patients (9.21%) the result was indeterminate.
Among the included patients, 80 patients (21%) had had a previous probable or confirmed SARS-CoV-2 infection, of whom 52 patients (66.7%) had a positive PCR. Of these, 27.8% (22 patients) had previous documented positive serology (IgG SARS-CoV-2).
The most frequent symptoms among these patients who had had the infection were fever (61.4%), general malaise (70.5%) and headache (64.1%). The duration of these symptoms averaged 17.04 days (SD: 21.16). In our experience, 19.23% of the sample (15 patients) required hospital admission due to COVID-19.
Among the 15 patients admitted, only 5 presented comorbidities. However, only 14 of our sample had comorbidity (HBP, DM, obesity, cardiovascular disease, COPD, asthma, chronic renal disease, personal history of cancer, etc.) and of these, 5 (35.7%) were admitted to hospital (p = 0.09). In the logistic regression analysis, HBP (OR 2.99, IC95% 0,3–21,9) and obesity (OR 4.15, IC95% 0,5–43,1) were shown to be significant.
Furthermore, it was not found that the percentage of patients requiring hospitalisation differed between those under treatment with biological and/or immunosuppressant drugs and others without these therapies (p = 0.16), with 12% of admissions being those with biological therapies.
The possibility of developing IgG antibodies against SARS-CoV-2 in patients with previous positive PCR was analysed. Among the 52 patients with documented positive PCR, only 34 patients (65.4%) had positive antibodies and 8 of them (15.3%) had indeterminate IgG titres (p = 0.53). Time between positive PCR and SARS-CoV-2 antibodies test was 169 days (median) (IQR: 85–329).
We obtained similar data when investigating the probability of developing antibodies in those patients with criteria of past infection (although not necessarily with a positive PCR test): 52 of the 80 patients (65%) had positive antibodies (and in 10 patients (12.5%) they were indeterminate), compared to 16 patients who had positive antibodies among those 305 (5.2%) with no history of COVID-19 infection, p = 0.0001.
One of the most important issues to analyse is the rate of seroconversion in patients who were on biologics or immunosuppressants.
When seroconversion was analysed among those patients under biological treatment, 13 patients of the 23 with previous positive PCR developed antibodies (56.5%), and in 4 cases the results were indeterminate (17.4%). However, when we analysed the influence of immunosuppressant treatment on the probability of developing antibodies among those patients with a previous positive PCR test, we identified that they were similar between those with or without treatment (77.8% vs 77.1%, p = 0.96).
We analysed the influence of biological treatment with anti-TNF on the possibility of developing antibodies, finding that among patients with a positive PCR test 54.5% (6/11 patients) developed antibodies when using anti-TNF drugs compared to 84% (20/33 patients) among those with any other treatment (p = 0.03).
Furthermore, when we compared the influence of the different types of biologic according to their therapeutic target, we identified that, overall, 38.9% (7/84 patients) of patients on anti-TNF had positive antibodies compared to 61.1% (11/37 patients) among those on Ustekinumab or Vedolizumab (p = 0.002) (Fig. 1).
Similarly, when we analysed seroconversion rates among patients with a previous positive PCR test, we found that it was 54.5% (6/11 patients) in the anti-TNF group versus 85.1% (6/7 patients) in the Vedolizumab or Ustekinumab group (p = 0.17).
Finally, we did not find that other baseline characteristics, such as sex, patient age or type of IBD, of the included patients were statistically significantly associated with antibody formation. However, when we analysed the influence of the patients’ work situation during the pandemic, we found that of those with in-person or semi in-person jobs 24.1% (35/145 patients) had positive antibodies compared to 16% (34/210 patients) who did not need to go to their workplace either because they were working remotely, were retired or unemployed (p = 0.05).
It should be noted that, of the 86 patients with associated comorbidity, 16 patients (18.6%) developed antibodies compared to 29% without the presence of comorbidity (p = 0.045).