Journal of Vaccine Research, 2025, Vol.15, No.1, 10-22 http://medscipublisher.com/index.php/jvr 15 system and influencing the generation and regulation of immune responses (Figure 2) (Garcia-Montero et al., 2021; Altomare et al., 2024; Dawson et al., 2025). The intestinal microbiota is rich in species and balanced in quantity, which can maintain the stability of the immune system, enhance the efficacy of vaccines, and also help preserve long-term immune memory by regulating the activity of immune cells and generating substances that affect inflammation and immunity (Nobs et al., 2020; Fan et al., 2023; Arifuzzaman et al., 2024). Figure 2 The nutrition-gut microbiota-immunity axis (Adopted from Dawson et al., 2025) Image caption: Schematic representation of nutrition, the gut microbiota and immune cells, along with the reciprocal interactions between each of these components (Adopted from Dawson et al., 2025) Adjusting the daily diet, such as eating more foods containing prebiotics and probiotics, or consuming more foods rich in dietary fiber, can improve the microbial environment in the intestines, enhance the body's ability to regulate immunity, and perhaps even make the immune effect of vaccines better (Conlon and Bird, 2014). If the balance among nutrient intake, intestinal microbiota and the immune system is disrupted, people will be more prone to illness or suffer from immune-related diseases. This fully demonstrates that maintaining the health of intestinal microbiota is crucial for achieving long-term immune protection (Fan et al., 2023; Arifuzzaman et al., 2024; Altomare et al., 2024; Dawson et al., 2025). 6 The Duration and Decline of Immunity 6.1 General trend of antibody decline over time After getting vaccinated, the number of antibodies usually reaches its peak within a few weeks and then gradually decreases over the following months. For instance, after receiving the COVID-19 mRNA vaccine, the antibody count can reach its peak around 21 to 28 days after the second dose. However, in the following 4 to 6 months, the antibody count will decrease by 55% to 95%. Moreover, this change has nothing to do with age, gender or the presence of other diseases (Goel et al., 2021; Notarte et al., 2021). Influenza vaccines also have a similar situation. The antibody count will increase one month after vaccination and start to decrease six months later. However, throughout the high-incidence season of influenza, they can still provide some protection (Doyon-Plourde et al., 2023). The rate and extent of antibody reduction vary from person to person, and there are also differences among different vaccines. The initial amount of antibody increase and the subsequent rate of reduction will both affect the duration of vaccine protection for the body (Antia et al., 2018). 6.2 Comparative analysis of the duration of immunization with different vaccines The duration for which various vaccines protect the body varies greatly. Vaccines like those for measles, rubella and smallpox cause the antibody count to decline very slowly after vaccination. Only 1% to 3% of people lose their protective effect every ten years. Diphtheria and tetanus vaccines can provide effective protection for most people for 25~50 years before antibodies start to decline rapidly (Antia et al., 2018). In contrast, the antibody count of the COVID-19 mRNA vaccine decreased more rapidly in the first six months. However, at this time, memory B cells and T cells in the body were still functioning (Notarte et al., 2021; Goel et al., 2021; Goel et al., 2022). The protective effect of the influenza vaccine will also significantly weaken within six months. However, if
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