Journal of Vaccine Research 2024, Vol.14, No.4, 196-206 http://medscipublisher.com/index.php/jvr 199 3 Immunogenicity of mRNA COVID-19 Vaccines 3.1 Short-term immunogenicity Short-term immunogenicity of mRNA COVID-19 vaccines has been extensively studied, showing promising results. In a phase 1 trial, the BNT162b2 vaccine demonstrated robust immunogenicity in both younger and older adults, with dose-dependent SARS-CoV-2-neutralizing geometric mean titers comparable to or higher than those observed in convalescent serum samples (Walsh et al., 2020). Similarly, a multicenter study reported that the BNT162b2 vaccine induced significant IgG antibody levels against SARS-CoV-2 spike proteins in the general population within 2-6 weeks after the second dose, achieving a 100% seropositivity rate (Furer et al., 2021). Moreover, the mRNA-1273 vaccine has shown comparable short-term immunogenicity. A meta-analysis revealed that a single dose of either mRNA vaccine (mRNA-1273 or BNT162b2) yielded antibody and neutralization titers similar to those in convalescent individuals (Naranbhai et al., 2022). These findings underscore the rapid and effective immune response elicited by mRNA vaccines shortly after administration, highlighting their potential in controlling the spread of COVID-19. 3.2 Long-term immunogenicity Long-term immunogenicity data for mRNA COVID-19 vaccines are still emerging, but initial findings are encouraging. A systematic review and meta-analysis indicated that mRNA vaccines maintain high efficacy and immunogenicity over time, with neutralizing antibodies against SARS-CoV-2 receptor-binding domains produced in over 90% of vaccinated individuals within 30 days of the first or second dose (Sharif et al., 2021). This sustained antibody response suggests that mRNA vaccines could provide long-lasting protection against COVID-19. In patients with autoimmune inflammatory rheumatic diseases (AIIRD), the BNT162b2 vaccine also demonstrated long-term immunogenicity, although at a reduced level compared to the general population. Despite lower seropositivity rates and IgG levels, the vaccine remained immunogenic in the majority of AIIRD patients, with stable disease activity post-vaccination (Furer et al., 2021). These findings highlight the potential for mRNA vaccines to offer durable immunity, even in populations with compromised immune systems. 3.3 Comparative immunogenicity Comparative studies have shown that mRNA vaccines generally elicit stronger immune responses than other vaccine platforms. For instance, a study comparing mRNA-1273, BNT162b2, and Ad26.COV2.S vaccines found that mRNA vaccines induced higher antibody concentrations and neutralization titers than the adenovirus-vectored Ad26.COV2.S vaccine (Naranbhai et al., 2022). Additionally, T-cell responses were more robust in recipients of mRNA vaccines compared to those who received the Ad26.COV2.S vaccine. Further supporting these findings, a systematic review and meta-analysis reported that mRNA vaccines provided higher protection against COVID-19 infection compared to adenovirus vector vaccines, with efficacy rates of 85% versus 73%, respectively (Sharif et al., 2021). This superior immunogenicity of mRNA vaccines underscores their effectiveness in generating a strong and lasting immune response, making them a critical tool in the fight against COVID-19. 4 Safety Profile of mRNA COVID-19 Vaccines 4.1 Immediate and short-term safety The immediate and short-term safety profile of mRNA COVID-19 vaccines has been extensively studied. In a phase 1 trial, BNT162b2 was associated with a lower incidence and severity of systemic reactions compared to BNT162b1, particularly in older adults. Common short-term adverse events included mild-to-moderate pain at the injection site, fatigue, and headache, with serious adverse events being rare and similar in both vaccine and placebo groups (Polack et al., 2020; Walsh et al., 2021). Another study reported that the mRNA-1273 vaccine showed moderate, transient reactogenicity, with the most common adverse events being injection-site pain, headache, and fatigue (Figure 2). No vaccine-related serious adverse events were reported (Baden et al., 2021; Creech et al., 2022).
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