I like to find articles like this one and share them with my friends because I find that I get my kids vaccinated (which I think is a positive thing) without asking any questions and it occurred to me last time when we went to the pediatrician that my oldest daughter was getting the same vaccine for the 3rd time. I think I get so distracted in doing this and that, that I forget to ask guestions. Well, I hope this helps answer a question that you didn't know you had!
In most cases, each shot creates only partial immunity to the disease, and subsequent shots build on that immunity. As a genreal rule for shots that come in a series, the first dose provides approximately 50 percent immunity, the second dose bumps it upu to about 75 percent, and the third dose given around 90 percent immunity. A few diseases require a fourth dose about a year after the third, and then another booster dose about four years later. These are necessary to keep immunity levels high enough to be effective.
Some shot, however, like those for measles, mumps, and rubella and chicken pox, don't require a whole series to create immunity. This is because they are live-virus vaccines, which work well with one inital dose and sometimes a booster years later.
Parenting Magazine december/janurary 2008 p. 48
