Journal of Vaccine Research 2024, Vol.14, No.6, 278-286 http://medscipublisher.com/index.php/jvr 280 3.2 Decline in antibody levels over time Antibody levels (anti-HBs) usually go down over time. Most people start losing some protection 5 to 10 years after getting vaccinated. In Canada, one study found that 82% of kids vaccinated at ages 8~10 had good antibody levels after five years, but only 68% still did after 15 years (Gilca et al., 2013). Figure 1 shows how antibody levels drop over 15 years. Even though they fall, most people still had some antibodies left. After getting a booster, their antibody levels quickly went back up. Figure 1 Anti-HBs titers distribution at different study time points (Adpoted from Gilca et al., 2013) Even when antibody levels fall below 10 mIU/mL (the level seen as "protected"), most people stay safe because their immune system remembers HBV (Wu et al., 2018; Ahonen et al., 2022). For example, in Israel, out of more than 20 000 people vaccinated as babies, only 0.004% got HBV even though 66% had no detectable antibodies after 15 years (Klinger et al., 2018). This shows just how important immune memory is. 3.3 Comparison between pediatric and adult vaccinees How long protection lasts also depends on when you got your shots. Kids who got vaccinated at birth often lose their antibodies faster than adults. That's probably because babies' immune systems aren't fully developed, so their first response is weaker (Lu et al., 2008). One study found that 63% of teenagers who were vaccinated as newborns had no detectable antibodies 15~18 years later. But after a booster shot, 89% of them had a strong immune response, meaning their immune memory was still working (Lu et al., 2008). Adults who get vaccinated later in life tend to keep their antibodies longer. A study from Beijing showed that 86% of adults still had good antibody levels one year after vaccination, and 54% still did after ten years. Overall, adults had higher antibody levels compared to kids (Shen et al., 2022). Because of these differences, it's important to keep checking on kids who got vaccinated early, especially as they grow up. Some kids, especially in high-risk groups, might need booster shots. But for low-risk groups, extra shots might not be needed. 4 Factors Influencing Long-Term Immunity Many things can change how long the hepatitis B vaccine keeps you safe. The dose you get, when you get the shots, how your body reacts, and if you have a weak immune system — all these matter. These things decide how strong your protection is and if you might need booster shots later.
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