Why has vaccination been successful against some diseases and not others?

Answer 1

Vaccines work by making your body create antibodies that fight off a specific pathogen (e.g., virus or bacteria). There are more vaccines for viruses today, but there are some for bacterial infections, too. The "Pneumonia Vaccine" is a vaccine against the bacteria Pneumococcus that is the one that most often causes pneumonia in the US.

Each viral vaccine is made to work for a specific virus or viruses, so viral strains that change form (mutate) frequently (like the common cold!) don't yet have a vaccine - or not one that lasts. Influenza viruses change, but more slowly than cold viruses, so we have a new flu vaccine every year. Typically the immunologists who study the flu look at what flu viruses are active in the Eastern parts of the world, like China where many types of flu originate and also look at the Southern Hemisphere during our summer and determine which strains are most likely to be here in the Northern Hemisphere by the time the flu season starts with colder weather in October. They pick the three most likely strains and usually one strain from each type of flu (A, B, and C) and begin production of that mix of virus antigens so they will be ready with the vaccine by fall. Some years they are better than others at predicting which strains will be in our outbreaks, but a good percentage of people are saved from illness or death each year using the seasonal flu vaccinations.