Diagnóstico serológico en pacientes tras infección por SARS-CoV-2. Estudio de neutralización en profesionales sanitarios tras vacunación

Abstract

Since December 2019, the world has experienced an unprecedented situation in recent history. From China, a hitherto unknown virus was spread. Sequencing its genome, it was soon related to the coronavirus family and received the name of SARS-CoV-2, and the disease it produced, COVID-19. It caused a pandemic with serious consequences for the economy and health around the world. During this time, considerable resources have been devoted, not only to diagnosing the population and treating the sick, but also to gathering as much information as possible about the virus in order to combat it. At this point, the production of anti-disease drugs, qualified health personnel and the development in record time of effective vaccines with technologies approved for the first time in history, such as messenger RNA vaccines, have been strengthened to stop the expansion of the virus. The aim of this thesis is to collect the most relevant information about SARS-CoV-2 and COVID-19 and to present the results obtained in the studies carried out at the San Cecilio Clinical University Hospital in Granada (Spain) on humoral immunity induced by the virus. In the first chapter, the production of anti-SARS-CoV-2 antibodies was characterised using serum samples from 1,236 patients admitted for COVID-19 and with SARS-CoV-2 infection confirmed by RT-PCR between April and July 2020 (first wave in Spain) in 18 healthcare centres in Spain and their production was determined based on age and sex. The determination of IgM + IgA and IgG antibodies was performed by ELISA techniques and showed that IgM + IgA had higher reactivity than IgG at the onset of the disease and up to 16 days later, being statistically significant one day after admission. The appearance of IgG was present from the seventh day after the positive PCR result and continued to increase three weeks later, when IgM + IgA and IgG reached similar values, and one month later, when IgG became the most prevalent. No significant differences were observed between men and women, but higher antibody production was observed at the beginning of the disease in patients under 75 years, although in subsequent samples, the results were equal in all age groups. In the second chapter, the in vitro capacity of antibodies generated against the SARSCoV- 2 wild-type strain and B.1, B.1.1.7 and B.1.351 variants after vaccination of healthcare workers at the San Cecilio Clinical University Hospital in Granada (Spain) with BNT162b2 was evaluated using a whole virus neutralisation assay. For this purpose, serum samples were collected from 99 healthcare workers (76 women, 23 men, with a mean age of 44 years) who received two doses of BNT162b2 vaccine between January and February 2021 (third wave in Spain), of whom only 11 had been previously exposed to SARS-CoV-2. Serum samples were collected coincident with the day of administration of each dose and 14 days later. Live whole virus of the wild-type strain and of B.1, B.1.1.7 and B.1.351 variants and Vero E6 cells were used. Results were obtained after microscopic observation of the cytopathic effect (CPE). After analysing the samples, it was observed that the pre-exposed group showed higher neutralisation titers after the first dose and a lower increase after the second dose, while the opposite was true for the non-pre-exposed group. In both groups, neutralisation against the B.1.1.7 variant reached values similar to those of the wild-type strain, but in the case of the B.1.351 variant, the neutralisation titers were lower.