It is expected that after chicken pox (varicella-zoster) vaccine that there is no more risk of acquiring the itchy rash. The truth is that the immunity may diminish with time. There is an increase in length of immunity when two doses of the vaccine are administered.
Some countries, like Australia, that don't include chicken pox as part of the required childhood immunizations have 90% of adults that are immune to the virus. Some studies show that 75% of adults have immunity to varicella-zoster virus in countries that require chicken pox immunization.
A chicken pox infection after immunization or natural exposure is often a milder infection. The virus doesn't leave the body but becomes dormant in some nerves and may become active again later in life. The wild virus stain is less likely to cause shingles in adults.
The vaccine was developed to prevent serious side affects of people at risk when there wasn't the medical technology to treat those side affects and serious infections. There are still deaths attributed to chicken pox infections but some deaths that would have been attributed to the varicella-zoster virus are now categorized under different categories.
This is because there are more advanced tests that can be done to determine the specific cause of death or serious illnesses. For example the rash from MRSA (methicillin-resistant Staphylococcus aureus) at one time may have been diagnosed as measles or chicken pox.
To get the maximum benefit of being immunized against Chicken pox and prevent an infection after receiving the vaccine, it is recommended that two doses be administered. The recommended immunization schedule is as follows:
Some people who are concerned about the side effects of the vaccine choose to have them given when the child is older and more able to handle the side affects.
There are a small percentage of people who get chicken pox from the virus in the vaccine. Some people may become infected with varicella-zoster when exposed to a different strain than the one that they developed immunity to. Others become immune from the virus strain in the immunization and after being exposed to wild strains of chicken pox, they have immunization to that stain as well and never get chicken pox.
The virus is always present after a chicken pox infection or from the virus being injected from an immunization, but becomes dormant and will reside in some nerves. Older adults over 60 years old may develop shingles when the virus becomes active again. It can be triggered by illness or treatment for a disease.
Those who get chicken pox after getting the vaccine are believed to get a milder version of the infection but may be more susceptible to shingles.
Learn about Chicken Pox In Adults.