Vaccines against viral infections are difficult to make to be 100% effective, even after a booster. The Chicken Pox vaccine is no exception. After one immunization, the vaccine confers immunity in approximately 85% of people. So approximately 15% of children and adults who are vaccinated can contract and manifest chicken pox if sufficiently exposed. However, the duration and intensity of the disease is significantly lessened.
Prior to the advent of the Chicken Pox vaccine, the disease was very common, with approximately 80% of children having the disease before they left elementary school. The average child had around 300 pox over their entire body, with each pox lasting 4-7 days and new pox erupting over a week’s time. Hence, the child was contagious for 7-10 days. Since the initiation of widesprerad vaccination, most children have not had the wild-type disease even after being exposed to an infected individual. If the person should contract the disease, the vaccinated individual will have, on average, just up to 50 pox with each lasting 2-4 days, with new pox erupting over 2-4 days. Therefore, there are significantly less lesions and the disease lasts about 4-7 days.
But where would the average person be exposed to wild-type chicken pox virus now that wide spread vaccination programs are in place? There is a long term reservoir of the disease in any person who has had the disease in the past. After a person has recovered from the Chicken Pox disease the virus never actually leaves the body. Instead, the virus goes dormant within the nerves of the body. During times of stress in the body, the virus can reactivate and cause a painful, itchy rash in the area where the nerve senses these sensations — called dermatomes. This is called Shingles or Zoster (short for Varicella zoster the name for the chicken pox virus). When a person has active shingles, those lesions are shedding active virus and thus that individual is contagious. So stay healthy and good luck!