Journal of Vaccine Research 2024, Vol.14, No.6, 278-286 http://medscipublisher.com/index.php/jvr 279 This study will focus on how long HBV vaccine protection lasts. It will look at different groups and ages to see how strong the immunity is. It will also check how the immune system works after vaccination and what can make protection weaker. The study hopes to help health workers and leaders make better vaccine plans and help reach the WHO goal to get rid of HBV by 2030. 2 Mechanism of Immunity Post HBV Vaccination After getting the hepatitis B vaccine, the body uses both antibodies and immune cells to fight the virus. These two work together to keep protection strong for a long time. 2.1 Humoral immune response The main job of the HBV vaccine is to help the body make antibodies against the hepatitis B surface antigen (anti-HBs). If a person's anti-HBs level reaches 10 mIU/mL or higher, it means they are protected and the vaccine did its job (Marshall et al., 2010). Antibody levels go up after the vaccine shots, but they slowly drop over time. Some people lose them faster than others (Chlibek et al., 2011). Even when the levels get low, the immune system can still react quickly if it sees the virus again or if a booster shot is given (Klinger et al., 2018). Long-term studies show that most healthy people stay protected for many years, even if their antibody levels become too low to measure (Gilca et al., 2013). 2.2 Cellular immunity T cells, a kind of immune cell, are also really important after getting the HBV vaccine. Even when no antibodies are found, the body still keeps memory B cells and T cells ready to fight HBV (Simons et al., 2016). Studies show that these T cells can stay active for decades and recognize parts of the virus when needed (Wu et al., 2011). That's why people who got vaccinated almost never get sick with HBV, even if their antibody levels fall (Madaliński et al., 2015). 2.3 Interaction between immune memory and exposure Sometimes, people naturally come into contact with HBV without getting sick. This helps keep their immune system alert. It happens a lot in places where HBV is common (Chaves et al., 2012). When this happens, memory B cells and T cells quickly react, and antibody levels can rise again for a short time (Wu et al., 2011). Booster shots can also wake up the immune system, even years after the first vaccination (Lu et al., 2008). This shows that immune memory is very important for staying protected for the long haul. In short, antibodies and immune cells, with the help of memory cells, work together to keep people safe after the HBV vaccine. Scientists are still working on better vaccine plans and trying to understand immune memory more deeply to help stop HBV around the world (Ma et al., 2019; Ciotti et al., 2020). 3 Duration of Immunity It's really important to know how long the hepatitis B vaccine can protect people. It helps us see how well the vaccine works to stop HBV and related diseases over time. Many things can change how long protection lasts, like when you get the shots, how your body reacts, and the vaccine schedule. 3.1 Longevity of protection in general populations Studies show that the HBV vaccine gives strong, long-lasting protection. It can stop infections and chronic HBV for many years. One review said over 95% of healthy people stayed protected for at least 30 years after finishing all their shots (Wu et al., 2011). In Taiwan, where they started giving the vaccine to kids early, the number of children with chronic HBV dropped from 10% to less than 1% over 30 years (Chen et al., 2015). In places where HBV is common, small exposures to the virus help keep people's immune systems active. For example, a 23-year study showed that 48% of people who got the vaccine as kids still had antibodies. Even better, 75% to 100% showed a strong immune response after getting a booster, proving that their immune memory was still working (Wu et al., 2011).
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