Researchers conducted a prospective study to assess the effectiveness of additional vaccine boosters in patients who received the initial SARS-CoV-2 vaccination series within the first year of the pandemic.
They assessed the temporal profile of cellular and serological responses in 639 individuals who received the SARS-CoV-2 vaccine. A significant portion of these individuals experienced a SARS-CoV-2 infection. At the time of their first vaccine dose, all participants were infection-free. The activation-induced Markers (AIM) assay was used to measure the proportions of SARS-CoV-2 Spike-specific T cells after each vaccine dose. Additionally, levels of circulating SARS-CoV-2 antibodies were determined through the Meso Scale serology assay.
The results showed a notable rise in SARS-CoV-2 Spike-specific CD4+ and CD8+ T cell reactions after the third dose of an mRNA vaccine against SARS-CoV-2 and improved CD8+ T cell responses post-fourth dose—moreover, older age correlated with a diminished response. Lastly, SARS-CoV-2 infection amplified cellular and humoral immune responses compared to vaccination alone.
Investigators concluded that repeated vaccinations enhanced T cell immunity, with both vaccination and natural infection contributing to maintaining population T cell levels, though these levels waned in older adults.