The effectiveness of vaccines is complicated
Dear Dr. Roach: I was wondering if you could explain why some vaccinations seem to completely protect against a disease, while others do not. For example, smallpox was completely eradicated by vaccination, and the hepatitis B vaccine is good for life and 98% to 100% effective, according to the World Health Organization. Yet we need to have the flu vaccine each year. I understand that is partly due to different strains of flu that come through, and of course we have the coronavirus vaccine, which ... I hope you can see where this question is going. I think an understanding of the vaccines we have and how they work would be extremely beneficial to all. -- M.S.
