(990) Monitored Covid-19 Vaccine Humoral Response in Immunocompromised Solid Organ Transplant Recipients

PURPOSE: COVID-19 infection continues to be a health threat particularly to immunocompromised transplant recipients. These patients remain at high risk for the development of severe disease. So, it was imperative to study the humoral response to COVID-19 vaccines in these patient to learn and to establish protocols or policies for the prevention and treatment of their infection. METHODS: We evaluated 90 sera from 36 heart and 34 from kidney transplant recipients for antibodies to COVID-19 (SARS-COV-2) following first, second or third vaccination. Antibodies were measured by 2 commercial methods of rapid test for qualitative detection of IgM and IgG or by single antigen beads. The latter was for semi-quantitative detection of IgG to RBD (receptor binding protein), S (Spike protein), S1 motif (receptor-binding domain that recognizes and binds to the host receptor angiotensin-converting enzyme 2) and S2 motif (mediates viral RNA to cell membrane fusion) of spike protein. RESULTS: Our finding demonstrates that almost half of the patients had no detectable antibodies by either of the methods. The single antigen beads assay was a better method in detecting antibodies with less false negative as compared to the rapid method. In patients who had developed antibodies to COVID-19, level of antibodies measured by MFI values increased after 2nd and 3rd dose of vaccinations. Of 18 patients who received the 3(rd) vaccine (first boost), 7 remained to have no detectable antibodies, 5 seroconverted to be positive and the other 6 demonstrated increase in their antibody levels. Interestingly, the titer of antibodies to S2 was lower than RBD, S and S1 and diminished more rapidly. In addition, patients who had both Covid-19 infection and vaccinations had higher level of antibodies to all, including the S2 motif. Furthermore, our data showed that patients with longer transplants demonstrated better humoral response to vaccines. CONCLUSION: COVID-19 vaccination in immunocompromised solid organ transplant recipients have resulted in detectable antibody response in almost half of the patients which is expected to be protective and prevent severe complications. Our observation supports the need to develop policies for mandatory vaccination prior to transplant as 39% of immunocompromised solid organ transplants had no detectable antibodies even after 3 doses of vaccine.