#4448 HUMORAL RESPONSE TO SARS-COV-2 AFTER FIVE SUCCESSIVE DOSES OF MRNA VACCINE AND PASSIVE IMMUNIZATION THERAPY IN STABLE KIDNEY TRANSPLANTATION PATIENTS Free

The poor humoral response after vaccination against SARS-CoV-2 in kidney transplant recipients (KT) led to the approval of new doses, the fifth being the last administered, and to the development of drugs for passive immunization. Our aim is to analyze the humoral immune response and the evolution of the antispike (antiS) antibody titer after 5 doses of mRNA vaccine against SARS-CoV-2 and the administration of pre-exposure prophylaxis.

We performed a prospective cohort study of stable KT patients from our center who received 5 doses of a mRNA vaccine from March 2021 to December 2022. KT recipients with less than 6 months after transplantation and with active oncological or hematologic disease were excluded. We determined antiS titers (Abbott SARS‐CoV‐2 IgG chemiluminescent microparticle immunoassay) at baseline and one month after the second, third, fourth and fifth doses. We consider seroconversion if antiS titer was greater than 260 BAU/mL. We compared humoral response after 2, 3, 4 and 5 doses.

We included 18 KT. Mean age was 59.8 years and 72.2% were male. The median time from KT to the first vaccine dose was 45 months, between the second and third 4 months and 6 months between the third and fourth and fourth and fifth doses. Seroconversion rate was 11.1% after 2 doses, 50% after the third, 72% after the fourth, and 94.4% after the fifth (p < 0.001). One TR did not develop antibodies after 5 doses. Two KT that had not seroconverted after the fourth also received passive immunization (tixagevimab-cilgavimab), maintaining high antiS titers 3 and 5 months after administration. The KT who seroconverted after 2 doses doubled the antiS titer after the third (1070 vs. 2168 BAU/mL; p = 0.180), in those who seroconverted after 3 doses it increased by 380% after the fourth (802 [587-2563] BAU/mL vs. 3116 [1004-5680] BAU/mL; p = 0.028) and in those who seroconverted after 4 doses, the antiS titer increased by 60% (1067 [100-2896] BAU/mL vs. 1762 [639-2684] BAU/mL) after the fifth (p = 0.213). No patients had neither acute rejection nor serious adverse effects.

Successive doses of vaccination increased the development and titer of antibodies against SARS-CoV-2 in KT. However the administration of new doses is necessary, especially bivalent vaccines, which increase protection against new variants of the virus. We should identify those patients who do not generate an adequate humoral response in order to offer them other prevention strategies.