Humoral activity was analyzed using ACCESS SARS-CoV-2 (Beckman Coulter Inc., Brea, CA, USA)a two-step enzyme chemiluminescent immunoassay (CLIA). both cohorts had been higher in convalescents (both before booster and 21 times after). The IgG titers had been subtly low in COVID-19 convalescents than in na?ve but without statistical significance. Data on cell-mediated immunity are scarce, especially with regard to the general population. A better understanding of the complexity of the immune response to SARS-CoV-2 could contribute to developing more effective vaccination strategies. Keywords: COVID-19, SARS-CoV-2, immune response, vaccinations, T-cell immune response, immunoglobulin G, interferon-gamma release tests, humoral immunity, cellular immunity 1. BRD4770 Introduction COVID-19 (Coronavirus Disease 2019) is a highly contagious illness caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), an unknown earlier pathogen belonging to the broad and diverse family of [1,2]. It emerged at the end of 2019 in Wuhan, and within just a few weeks it spread throughout the world. Speed of transmission and its severe medical, social, and economic consequences led the World Health Organization (WHO) to the decision to pronounce, on 11 March 2020, COVID-19 a pandemic [3]. As BRD4770 of 8 September 2022, SARS-CoV-2 has contributedaccording to the official datato 603 711 760 BRD4770 confirmed cases and 6 484 136 deaths worldwide [4]. Today, over 2.5 years since the first case was reported in China, the COVID-19 pandemic is far from over. Moreover, its complex and long-term implications still constitute a great challenge for public health, the global economy, and politics [5]. Since the pandemics beginning, intensive research has been conductedboth on individual and population levelson the changing SARS-CoV-2 molecular structure and properties of circulating and emerging variants in terms of their transmissibility, impact on immunity, and severity of infection they cause [6,7]. Simultaneously, numerous trials have BRD4770 been performed to understand different manifestations and courses of COVID-19 (depending on the variant that caused it) and find the most optimal methods of prevention and treatment [8,9]. A significant breakthrough in preventing the virus spread and altering the pandemic trajectory the world sought was achieved in the development and rollout of COVID-19 vaccines [10,11]. BRD4770 The first vaccines outside clinical trials were administered in the United Kingdom on 8 December 2020 [12]. The first products available on the market were based on using part of viral mRNA containing nucleoside-modified RNA (modRNA) in lipid nanoparticles, encoding the SARS-CoV-2 full-length spike glycoprotein (mRNA-1273, Moderna; BNT162b2, Pfizer/BioNTech; BNT). Another vaccine type available for the public at that time was based on the replication-deficient chimpanzee adenoviral vector, containing the SARS-CoV-2 structural surface glycoprotein antigen gene [7,13,14] (ChAdOx1-S (recombinant), the Oxford/AstraZeneca; ChAd) [15,16]. All products mentioned above were approved for use as a two-dose primary course. Although vaccination is still considered the most effective defense strategy against SARS-CoV-2, multiple long-term follow-ups of vaccinated individuals conducted within clinical trials and real-world settings revealed that immune response to COVID-19 is waning over time [17,18,19]. Decreasing immunity has also been observed in individuals with COVID-19 history [20]. Moreover, numerous epidemiological studies report re-infections in vaccinated na?ve subjects and both vaccinated and non-vaccinated convalescents [21,22]. In addition, a growing body of evidence indicates that particular population groups mount a limited or undetectable immune response to SARS-CoV-2 vaccines [23]. Low or non-responsiveness to COVID-19 inoculation can be related to, i.a., genetics, overall physical and mental health (i.a., stress), immune status, and presence of particular conditions (i.a., autoimmune and inflammatory diseases), such as advanced age and immunosenescence [23,24,25]. Those observations led to the introduction of a booster dose of the vaccineto restore the protection against COVID-19-related serious outcomes. According to the current recommendations, it should be administered, depending on the product received during the initial series, optimally 4C6 months after completing the primary vaccination course [26,27,28]. Although the homologous strategy is still considered standard practice, due to changes in public health vaccination policy, and problems with vaccines availability, starting from Spring 2021, many countries decided to apply a heterologous booster [29,30]. Such an approach was initially documented as augmenting immune responses with tolerable reactogenicity [31,32,33]. The Rabbit Polyclonal to Androgen Receptor (phospho-Tyr363) primary aim of active immunization.