> The HB vaccine unfortunately doesn't work that well, many people are still not fully immune even after several doses

This is incorrect. The HBV vaccine is one of the most effective vaccines available for any pathogen, providing full immunity to over 95% of healthy infants, children, and young adults, and with that immunity typical lasting for at least 30 years (and likely for life).

If someone is one of the rare exception, tthat's easy to detect with blood titers, and the response is either to give them additional doses or to deliver an adjuvanted version (which is the same thing regularly done for other vaccines which are either less effective or primarily targeted at the elderly, who have weaker immune responses).