Journal of Vaccine Research 2024, Vol.14, No.4, 196-206 http://medscipublisher.com/index.php/jvr 201 BNT162b2 vaccine was immunogenic in the majority of patients with AIIRD, with an acceptable safety profile. However, treatments with glucocorticoids, rituximab, mycophenolate mofetil (MMF), and abatacept were associated with reduced immunogenicity (Furer et al., 2021). In children aged 6 to 11 years, the mRNA-1273 vaccine was found to be safe and effective, with no vaccine-related serious adverse events reported. The most common adverse events were low-grade and transient, such as injection-site pain, headache, and fatigue (Creech et al., 2022). Another systematic review highlighted that inactivated vaccines had a more satisfactory safety profile compared to mRNA vaccines in adolescents and children, although the latter still showed acceptable safety and immunogenicity (Du et al., 2022). 5 Comparative Effectiveness with Other Vaccine Types 5.1 Efficacy comparisons The efficacy of mRNA COVID-19 vaccines has been extensively compared with other vaccine types, including adenoviral vector vaccines and heterologous prime-boost schedules. The BNT162b2 mRNA vaccine demonstrated a high efficacy of 95% in preventing COVID-19 in individuals aged 16 years and older, with consistent efficacy across various subgroups defined by age, sex, race, ethnicity, and baseline health conditions (Polack et al., 2020). In contrast, the adenoviral vector vaccine Gam-COVID-Vac (Sputnik V) showed an efficacy of 91.6% in a large cohort during its phase 3 trial (Logunov et al., 2021). A meta-analysis comparing the immunogenicity and effectiveness of mRNA-1273, BNT162b2, and Ad26.COV2.S vaccines found that mRNA vaccines generally produced higher antibody concentrations and neutralization titers compared to the adenoviral vector vaccine Ad26.COV2.S (Naranbhai et al., 2022). Additionally, a systematic review and network meta-analysis indicated that a three-dose mRNA regimen was the most effective against both asymptomatic and symptomatic COVID-19 infections, with a vaccine effectiveness of 96% (Au and Cheung, 2022). 5.2 Safety comparisons Safety profiles of mRNA vaccines have been favorable, characterized by mild-to-moderate short-term side effects such as pain at the injection site, fatigue, and headache. Serious adverse events were rare and similar between the vaccine and placebo groups (Polack et al., 2020). In comparison, the adenoviral vector vaccine Gam-COVID-Vac also showed a good safety profile, with most adverse events being mild and not related to vaccination (Logunov et al., 2021). Heterologous prime-boost schedules, which combine different vaccine types, have shown increased reactogenicity compared to homologous schedules. For instance, the Com-COV study reported higher systemic reactogenicity, such as feverishness and fatigue, in heterologous schedules involving ChAdOx1 nCoV-19 (ChAd) and BNT162b2 (BNT) compared to homologous schedules (Liu et al., 2021a; Liu et al., 2021b; Shaw et al., 2021). However, these adverse events were generally mild and transient. 5.3 Heterologous vaccination schedules Heterologous vaccination schedules, which involve administering different types of vaccines for the prime and boost doses, have been explored to enhance immunogenicity and address vaccine supply issues. The Com-COV study found that the ChAd/BNT heterologous schedule produced higher SARS-CoV-2 anti-spike IgG concentrations compared to the homologous ChAd/ChAd schedule, supporting the flexibility of using heterologous prime-boost vaccination (Liu et al., 2021a; Liu et al., 2021b). A systematic review and network meta-analysis also highlighted the effectiveness of heterologous boosting, particularly with mRNA vaccines, which showed satisfactory vaccine effectiveness of 88% when used as a booster following two doses of an adenoviral vector vaccine (Au and Cheung, 2022). Additionally, population-based cohort analyses in Nordic countries during the Omicron variant predominance indicated that heterologous booster schedules provided increased protection against severe COVID-19 outcomes compared to primary schedules and were comparable to homologous mRNA booster schedules (Andersson et al., 2023).
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