Background: Response to Covid vaccine among transplant recipients remains diminished comparing to general population. Here, we assessed safety and effectiveness of the Covid vaccination in the protection from the Covid infection and in the induction of the SARS-CV-2 Spike total antibody (Spike ab) in islet transplant recipients.

Methods: We analyzed immune response to Covid-19 and COVID-19 vaccination in a cohort of 20 islet transplant recipients: N=13 after islet transplant alone (ITx), N=7 with islet after kidney (IAK) or pancreas after islet graft (PAI). The median age was 48 years (25-62). Maintenance immunosuppression included tacrolimus and an antimetabolite in addition to 5mg of Prednisone in IAK and PAI recipients. Four patients got booster.

Results: Seven patients (38%) chose not to be vaccinated and 5 (71%) of them remained Covid-19 free with no Spike ab present in their blood. The other two patients (29%) had only mild symptoms of COVID-19 infection with Spike ab detected afterwards (46U/ml -IAK and 180U/ml- ITx). In contrast, all remaining 13 patients (62%), who received vaccination: N= 8 Pfizer, N=4 Moderna, N=1 J&J while on immunosuppression for a median of 7 years (0.5-16), remained Covid-19 free based on lack of symptoms and PCR testing (p=0.11, Fischer). The level of Spike ab in response to vaccine varied: undetected- (N=4), range- 5-40U/ml (N=4), range around 75U/ml (N=2), around 400U/ml (N=2), and above 2,500U/ml (N=1). Presence of 5mg of Prednisone did not affect the outcomes. None of the patients experienced moderate/serious adverse events related to the vaccination. Booster administered 4-6 months after the second dose of the vaccine increased the level of Spike ab from 22, 92, 441 to over 2,500 in all 3 patients, respectively. One patient who did not developed any Spike ab after Pfizer vaccine, also did not respond to the booster. Islet graft function remained stable in all patients during  8-12 months after initial vaccination. There were no SAEs related to the vaccination or booster.

Conclusion: One third of unvaccinated islet transplant recipients developed Covid-19, however, all of them presented only with mild symptoms. In contrast, none of vaccinated transplant patients developed COVID-19 infection with 69% rate of seroconversion after vaccination. Booster increased level of the Spike ab in those patients who responded to the original vaccination.