Introduction: The humoral response to COVID-19 vaccines in transplant recipients has been reported to be lower than the obtained in the general population. For the Pfizer vaccine, an antibody response in 5-59% of those vaccinated is described, depending on the immunosuppressive maintenance therapy implemented, with a 56% of cellular response after the 2nd dose of the vaccine. The clinical significance of this poorer immune reaction is unclear. On the other hand, the degree of response to the Sinovac vaccine, the most used early in Chile, is unknown. Taking into account that the lethality of SARS-CoV-2 infection in transplanted patients was 6 times higher than the general population during the first wave of the pandemic (renal FUTAC data), we carried out this study with the aim of knowing the clinical effectiveness of  the first two vaccines implemented in Chile in kidney transplant patients.

Methods: Prospective, observational, multicenter study. The FUTAC database was available with a periodic report from all transplant centers in the country with 98% coverage and information available from 3/27/2020 to 7/7/2021. The data of transplanted patients who were infected with SARS-COV-2 were recorded comparing between those who had been fully vaccinated or not, with the Sinovac or Pfizer vaccine, evaluating the incidence of hospitalization and lethality. The group with complete vaccination was defined if the infection occurred 15 days after the second dose and the unvaccinated group corresponded to those without vaccination, with incomplete vaccination or in a period < 15 days after the second dose.

Results: Of a total of 424 cases, 16 were discarded due to incomplete data, analysing 408 patients, of which 336 (82%) suffered the infection without being effectively vaccinated and 72 (18%) who were fully vaccinated. Of the total patients fully vaccinated, 57% (40/70) received Sinovac vaccine and 43% (30/70) Pfizer. No differences were found between COVID-19 infection rates between 2020 and 2021. Of the fully vaccinated patients, 42/72 (58%) were hospitalized, and 14/72. (19%) died; in this group, there are 7 patients who are alive but seriously ill at the time of closing the registry. In the unvaccinated group, 53% (179/336) were hospitalized and 15% (50/336) died, without significant differences in hospitalization or fatality rates. No differences were found in hospitalization or fatality rates between those vaccinated with Pfizer or Sinovac.

Conclusions: The transplanted population, although fully vaccinated, maintains a high fatality rate, which is still 6 times higher than the general population. Although these data could be biased by the patients who did not consult, they were an input to decide a third dose of vaccination just applied to this highly vulnerable population, whose results are waiting to be evaluated. In Chile, the third booster dose was started in September 2021 and a 4th booster dose is currently being delivered starting in January 2022.