From the Guidelines
Losing immunity to chicken pox following vaccination is uncommon, but breakthrough infections can occur, and a second dose of varicella vaccine is recommended to enhance immunity and prevent outbreaks. The varicella vaccine provides strong protection initially, with about 85% of people maintaining immunity long-term 1. However, some vaccinated individuals may experience breakthrough infections, typically with milder symptoms than unvaccinated people.
Key Points
- The vaccine effectiveness for prevention of disease of any severity has been 80% to 85% 1
- A large number of cases of varicella continue to occur among people who already have received the vaccine (breakthrough varicella) 1
- Outbreaks of varicella have been reported among highly immunized populations of schoolchildren 1
- The peak age-specific incidence has shifted from 3- to 6-year-old children in the prevaccine era to 9- to 11-year-old children in the postvaccine era for cases in both immunized and unimmunized children during these outbreaks 1
- After administration of 2 doses of varicella vaccine in children, the immune response is markedly enhanced, with .99% of children achieving an antibody concentration of $5 U/mL (an approximate correlate of protection) and a marked increase in geometric mean antibody titers after the second vaccine dose 1
- The estimated vaccine efficacy over a 10-year observation period of 2 doses for prevention of any varicella disease is 98% (compared with 94% for 1 dose), with 100% efficacy for prevention of severe disease 1
- Recipients of 2 doses of varicella vaccine are 3.3-fold less likely to have breakthrough varicella, compared with those who are given 1 dose, during the first 10 years after immunization 1 To ensure optimal protection, the recommended vaccination schedule includes two doses: the first at 12-15 months of age and the second at 4-6 years. For adults who were previously vaccinated but are concerned about waning immunity, a blood test called a varicella-zoster virus (VZV) antibody titer can determine if immunity persists. If immunity has significantly decreased, a booster dose may be recommended, particularly for healthcare workers or those at high risk of exposure 1. The vaccine works by introducing a weakened form of the virus, stimulating the immune system to produce antibodies and memory cells that recognize and fight the virus if exposed in the future. While immunity may decrease somewhat over decades, most vaccinated individuals retain significant protection against severe disease.
From the Research
Loss of Immunity to Chicken Pox Following Vaccination
- The study 2 presents a case of a 29-year-old woman who received three doses of the varicella-zoster (VZV) vaccine but continued to have a negative antibody titer as measured by a commercial ELISA assay.
- Despite the negative antibody titer, the woman did not develop clinical chicken pox after three direct contacts with infectious children, suggesting that she may have had some level of immunity.
- A lymphocyte proliferation assay was performed, which showed that the patient had a varicella stimulation index (SI) of 46.5, indicating a cell-mediated response to the vaccine.
- The study suggests that in some individuals, the antibody response to the VZV vaccine may be low despite an adequate cell-mediated response, and that commercial VZV ELISA assays may not be sensitive enough to detect lower titers induced by the vaccine.
- The use of more sensitive assays, such as fluorescent antibody to membrane antigen and latex agglutination, verified the presence of VZV-specific IgG in the patient, highlighting the importance of using multiple measures to assess immunity.
- The study implies that repeated immunizations and more sensitive measures of VZV-specific IgG should be used to validate protection, rather than relying solely on commercial ELISA assays 2.