Researchers from the University of Birmingham and Public Health England have conducted a study on the dynamics of immune responses in elderly people who have received two doses of the Pfizer/BioNTech COVID-19 vaccine at a standard or extended interval. The study currently published on a pre-print server revealed that an extended interval vaccination can enhance the humoral immune response by 3.5-fold.
The study was initially started with 172 individuals aged 80 years and above. Of all participants, 99 received the two doses of BNT162b2 vaccine at an interval of 3 weeks (standard interval); whereas, 73 participants received the two doses at an interval of 11 – 12 weeks (extended interval). However, in the final cohorts, 10 participants from the standard interval group and 5 participants from the extended interval group were excluded as they were seropositive against SARS-CoV-2.
The serum samples obtained from the vaccinated participants were analyzed for spike-specific antibodies to determine the intensity of the humoral immune response. Similarly, to determine the cellular immune response, peripheral blood mononuclear cells were isolated from whole blood samples and analyzed for interferon-γ secreting T cells. For the analysis, blood samples were collected at two time points. For participants who were vaccinated at a standard interval, the blood samples were collected at 2 – 3 weeks (peak response) and 8 – 9 weeks (durable response) after the 2nd dose. For participants with an extended interval regimen, blood samples were taken at 5 -6 weeks after the 1st dose and 2 – 3 weeks (peak response) after the 2nd dose. In the standard interval group, spike-specific antibodies were detected in 100% of participants at both time points. Among the participants, a peak antibody response was observed after the 2nd dose, followed by a 2.6-fold reduction over the subsequent weeks.
In the extended interval group, antibodies were detected in 91% and 100% of participants at the 1st and 2nd-time points, respectively. Among the participants, a 242-fold increase in antibody response was observed after the 2nd vaccine dose compared to the 1st dose. By comparing the robustness of humoral immunity after the 2nd vaccine dose, 3.5-fold higher antibody response was observed in participants who were vaccinated with the extended interval regimen. Among participants in the standard interval group, about 60% exhibited spike-specific T cell response 2 – 3 weeks after the 2nd dose. However, after 8 – 9 weeks, only 15% of them showed T cell response. In contrast, only 8% of participants in the extended interval group demonstrated T cell response after the 1st dose. However, the proportion of participants increased to 31% after the 2nd vaccine dose.
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