Introduction: The capacity of different anti-SARS-CoV-2 vaccines to elicit immune response is not equivalent in the healthy population compared to chronically immunosuppressed patients. Most of the reports available so far to assess the effects of anti-SARS-CoV-2 vaccines on solid organ transplant recipients (SOTR) were performed using mRNA-based vaccines. The majority of the vaccines used so far in our country are adenovirus-vector vaccines (Sputnik V and Covishield/AstraZeneca-Oxford).  Goal:  to assess the seroconversion after vaccination with the non-replicative vector-based vaccines after transplantation.

Methods: Seventy-nine patients of liver transplant (79), combined liver-intestine transplant (1) or intestinal/multivisceral transplant (4) receiving their first vaccine dose between March and June 2021 were included, mean age of was 55,6 years old (range 18-75,9; 71% males). All patients have a post-transplant follow up longer than 1 year (median 6 years, range 1-25 years). Samples after second and third doses were also analyzed, in all cases obtained at least three weeks after last vaccination. Patients serological status was evaluated using three different anti-S commercial ELISA kits and an in-house made anti-N ELISA. Patients with previous PCR-confirmed COVID19 were excluded.

Results: We found that 28,1% of patients (9 out of 32) seroconverted after a single dose of Sputnik V (8 out of 21) or Covishield (1 out of 11), whereas 18 out of 27 (66,7%)  seroconverted after second dose of Sputnik V (7 out of 10) or Covishield (11 out of 17) and 12 out of 13 seroconverted after a third dose (92%), most of them have received two doses of Sputnik V and receiving Moderna, Pfizer or Covishield as third dose. There is a significant difference in the proportion of seroconversion between the groups that received one dose or two doses of vaccine (p<0.005, Chi square test) whereas the difference is not significant between groups receiving two and three doses (p=0.08, Chi square test). The comparison between responder’s and non-responders to the single dose vaccine showed no differences in either patient age, post-transplant time, days after vaccination, presence of comorbidities and maintenance immunosuppressive therapy.

Conclusion: Despite having a lower seroconversion rate compared to the general population, viral-vector vaccines benefit SOTR patients increasing the seroconversion rate using at least two doses of vaccine. These results support the concept of developing tailor-made vaccination guidelines for this specific population.