MO997: Covid-19 Antibody Responses in Renal Transplant Patients Following Booster Vaccination
Authors: Lavery Grace , Floyd Lauren , Solomon Laurie , Dhaygude Ajay 
Published: May 2022

Abstract

BACKGROUND AND AIMS
The COVID-19 vaccination programme has been monumental in the protection against SARS-CoV-2 infection. However, recent research has shown suboptimal responses in immunosuppressed patients, such as those with solid organ transplant receiving immunosuppressive (IS) treatment. Whilst initial studies have suggested patients have improved humoral response to booster vaccines, the data are still limited [1]. We have examined the differences in SARS-CoV-2 anti-spike antibodies in renal transplant patients between second and third doses of the vaccine and aimed to determine if those that had a poor response to the initial vaccine course developed adequate immunity following booster vaccination.

METHOD
A cohort study of 63 renal transplant patients receiving immunosuppression was constructed from a single centre between December 2020 and December 2021. All patients received a full course of the UK government approved SARS-CoV-2 vaccine as well as a third booster dose. Enzyme-linked immunosorbent assays for SARS-CoV-2 anti-spike antibodies were carried out and titres of ≥0.8 U/mL were considered reactive.

RESULTS
Of the 63 patients included, the median age was 55 years (IQR: 44–66). All patients received three doses of the SARS-CoV-2 vaccine and anti-spike antibodies were checked 32.2 ± 17 days following the third dose. Thirty-eight patients received two doses of Oxford-AstraZeneca followed by one dose of Pfizer-BioNTech. Twenty-five patients received three doses of Pfizer-BioNTech.
46.0% (n = 29) of patients had a detectable antibody response following two doses of the vaccine and 87.3% (n = 55) had a discernible response following the booster. The average titre value rose by 201% between the second and third doses. Eight patients had undetectable antibodies following the second dose and half (n = 4) developed evidence of humoral immunity following the booster. Whilst increasing age and shorter time from transplantation was associated with poor humoral response to both second and third doses, it did not reach statistical significance; P = 0.29, P = 0.059 respectively. Ten patients had previous COVID-19 infection: 2 remained seronegative following 3 vaccines, and both were within 12 months of transplantation. Those receiving calcineurin inhibitors (CNI) and antimetabolite treatment were associated with lower antibody titres compared with those receiving CNI alone (Table 1).

CONCLUSION
We have shown that despite three doses of the vaccine, some high-risk renal transplant patients remain vulnerable to COVID-19 and fail to develop an adequate humoral response to the vaccine. Time from transplantation and IS medications have a significant effect on SARS-CoV-2 anti-spike antibody production. Whilst some studies have suggested those with solid organ transplants mount a lower immune response to mRNA based vaccines [2], our cohort did not demonstrate this difference. Going forward there are still a number of unanswered questions about the significance and effectiveness of COVID antibodies, as well as the long-term protection they offer [3]. Developing ways in which we can protect those with poor humoral response despite repeated vaccination is vital.