4 ms·
No vaccine has ever been 100% effective, and waning immunity has always been a common phenomenon. Some flu vaccines are only about 50% effective. Polio, tetanu
by mbrubeck 5y ago
No vaccine has ever been 100% effective, and waning immunity has always been a common phenomenon. Some flu vaccines are only about 50% effective. Polio, tetanus, hepatitis, and smallpox vaccines have all required booster doses due to waning immunity.