Neutralising reactivity against SARS-CoV-2 B.1.617.2 (Delta) variant by vaccination status and pre-exposure

Abstract

In February and March 2020, one of the first Italian clusters of SARS-CoV-2 infection was detected in the municipality of Vo’. Positive subjects were followed up at 2 and 9 months post-infection with different immuno-assays and a micro-neutralisation test. Here we report on the results of the third serosurvey conducted in the same population in June 2021, 15 months post-infection, when we tested 61% of the infected individuals (n=76). Antibodies against the spike (S) antigen significantly decreased (P<0.006, Kruskal-Wallis test) among unvaccinated subjects (n=35) and increased (P<0.0001) in vaccinated individuals (n=41), whereas those against the nucleocapsid (N) decreased in the whole cohort. From the comparison with two control groups (naïve Vo’ inhabitants (n=20) and healthcare workers (HCW, n=61)), subjects vaccinated post exposure (hybrid immunity) had higher antibody levels (P<0.0001) than subjects vaccinated when naïve. Two doses of vaccine elicited stronger anti-S antibody response than natural infection (P<0.0001). Finally, the neutralising reactivity of sera against the B.1.617.2 (Delta) was lower than compared to the B.1 strain (median 1:320 versus 1:1280 1/dil, P<0.0001, and 1:640 versus 1:2560 1/dil, P=0.0014, after one or two vaccine doses, respectively), although subjects with hybrid immunity maintained neutralising titres above 1:40 1/dil.

Longitudinal analysis of T cell receptor repertoires reveals shared patterns of antigen-specific response to SARS-CoV-2 infection

“…However it is unlikely that these differences could explain the significant increases in clonal depth and breadth observed after vaccination. A similar trend was observed in antibody levels (24), and this further supports the vaccine-related changes observed in T cells.…”

“…Despite the limitations discussed above, our data suggest that T cells represent another key component of the adaptive immune response that correlates with important clinical factors, including disease severity. Mounting evidence also suggests that, while antibody-derived immunity is severely impacted by SARS-CoV-2 evolution (23,24,48), the T cell response may be more robust against viral variants (25,47,49). Though tools exist to study T cells in a research setting, they remain difficult to quantify accurately at population scale (50).…”

“…Several studies have also shown that the T cell response is diverse, targeting regions across the viral genome, while the B cell response is concentrated against spike protein (17)(18)(19)(20)(21)(22). These findings likely underlie recent observations that protection against the virus induced by vaccination remains high against recent emerging variants such as Delta and Omicron, despite large reductions in neutralizing antibody (NAb) titers against these variants (23)(24)(25)(26). Finally, genetic factors influencing antigen presentation to T cells have also been shown to impact disease severity (27).…”