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2. Immunity Naturally Declines
Protection generated by vaccination is strongest during the months following immunization. Over time, antibody levels gradually decrease.
Although immune memory remains active, declining antibody concentrations can make infection more likely, particularly when exposure levels are high.
3. Individual Immune Responses Differ
Not everyone develops identical protection after vaccination. Age, underlying medical conditions, medications, and overall immune function can influence how strongly a person responds to a vaccine.
Some individuals may remain more vulnerable to infection despite being vaccinated.
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