Chickenpox is prevalent among children. In addition, there have been cases of secondary infection in the home that have spread to adults.
The chickenpox vaccine is essentially a vaccine whose effectiveness wears off over time. Breakthrough infection with chickenpox can occur even after the chickenpox vaccine is administered. It is known that 1.6 out of approximately 1,000 people will contract the real chickenpox virus 1 year after vaccination, 9.0 out of 1,000 people after 5 years, 20.4 out of 1,000 people after 8 years, and 58.2 out of 1,000 people after 9 years, even after two doses of the vaccine.
Human immunity is gradually suppressed as we age. It is well known that immunity to various infectious diseases, especially to the varicella virus, declines with age. Conversely, immunity to infectious diseases is thought to be stimulated by frequent exposure to many sources of infection.
Most people are extremely susceptible to chickenpox breakthrough infection and shingles as a result of losing contact with many viruses, including the varicella virus, for a period of four years or more. In particular, the rate of breakthrough infection among children and students is likely to be much higher than it was in 2007, when the above study was conducted.
(Currently, no additional Varicella vaccination is recommended for children or students; two doses of Singrix ®︎ are recommended for those over 50 years of age.)
Waning of varicella immuniry
Heterogeneity of memory T cells in aging