<unk>  is 70% to 90% effective for preventing<unk>  and more than 95% effective for preventing severe<unk> . Follow-up evaluations have taken place in the United States of children immunized that revealed protection for at least 11 years. Studies were conducted in Japan which indicated protection for at least 20 years. People who do not develop enough protection when they get the vaccine may develop a mild case of the disease when in close contact with a person with chickenpox. In these cases, people show very little sign of illness. This has been the case of children who get the vaccine in their early childhood and later have contact with children with chickenpox. Some of these children may develop a mild chickenpox also known as breakthrough disease. Another vaccine, known as zoster vaccine, is simply a larger-than-normal dose of the same vaccine used against chickenpox, and is used in older adults to reduce the risk of shingles (also called herpes zoster) and postherpetic neuralgia, which are caused by the same virus. The live zoster (shingles) vaccine is recommended for adults aged 60 years and older. A recombinant zoster (shingles) vaccine is recommended for adults aged 50 years and older. Duration of immunity The long-term duration of protection from<unk>  is unknown, but there are now persons vaccinated twenty years ago with no evidence of waning immunity, while others have become vulnerable in as few as six years. Assessments of duration of immunity are complicated in an environment where natural disease is still common, which typically leads to an overestimation of effectiveness. Some vaccinated children have been found to lose their protective antibody in as little as five to eight years. However, according to the World Health Organization (WHO): "After observation of study populations for periods of up to 20 years in Japan and 10 years in the United States, more than 90% of immunocompetent persons who were vaccinated as children were still protected from<unk> ." However, since only one out of five Japanese children were vaccinated, the annual exposure of these vaccinees to children with natural chickenpox boosted the vaccinees' immune system. In the United States, where universal<unk> tion has been practiced, the majority of children no longer receive exogenous (outside) boosting, thus, their cell-mediated immunity to VZV<unk>  zoster virus) wanes—necessitating booster chickenpox vaccinations. As time goes on, boosters may be necessary. Persons exposed to the virus after vaccination tend to experience milder cases of chickenpox if they develop the disease. Catching "wild" chickenpox as a child has been thought to commonly result in lifelong immunity. Indeed, parents have deliberately ensured this in the past with "pox parties". Historically, exposure of adults to contagious children has boosted their immunity, reducing the risk of shingles. The US Centers for Disease Control and Prevention (CDC) and corresponding national organizations are carefully observing the failure rate which may be high compared with other modern vaccines—large outbreaks of chickenpox having occurred at schools which required their children to be vaccinated. Chickenpox Prior to the widespread introduction of the vaccine in the United States in 1995 (1986 in Japan and 1988 in Korea), there were around 4,000,000 cases per year in the United States, mostly in children, with typically 10,500–13,000 hospital admissions (range, 8,000–18,000), and 100–150 deaths each year. Most of the deaths were among young children. During 2003, and the first half of 2004, the CDC reported eight deaths from<unk> , six of whom were children or adolescents. These deaths and hospital admissions have substantially declined in the US due to vaccination, though the rate of shingles infection has increased as adults are less exposed to infected children (which would otherwise help protect against shingles). Ten years after the vaccine was recommended in the US, the CDC reported as much as a 90% drop in chickenpox cases, a<unk> -related hospital admission decline of 71% and a 97% drop in chickenpox deaths among those under 20. Vaccines are less effective among high-risk patients, as well as being more dangerous because they contain attenuated live virus. In a study performed on children with an impaired immune system, 30% had lost the antibody after five years, and 8% had already caught wild chickenpox in that five-year period. Herpes zoster Herpes zoster (shingles) most often occurs in the elderly and is only rarely seen in children. The incidence of herpes zoster in vaccinated adults is 0.9/1000 person-years, and is 0.33/1000 person-years in vaccinated children; this is lower than the overall incidence of 3.2–4.2/1000 person-years. Adult shingles cases may increase after introduction of<unk> , but evidence is unclear. While research using computer models has tended to support the hypothesis that vaccination programs would increase incidence of zoster in the short term, the evidence from epidemiological studies is mixed, and increases observed in zoster incidence in some studies may not be related to vaccination programs, as the incidence increases prior to the<unk>  program being initiated. Regarding herpes zoster, the CDC stated in 2014: "Chickenpox vaccines contain weakened live VZV, which may cause latent (dormant) infection. The vaccine-strain VZV can reactivate later in life and cause shingles. However, the risk of getting shingles from vaccine-strain VZV after chickenpox vaccination is much lower than getting shingles after natural infection with wild-type VZV." Schedule The WHO recommends one or two doses with the initial dose given at 12 to 18 months of age. The second dose, if given, should occur at least one to three months later. The second dose, if given, provides the additional benefit of improved protection against all<unk> . This vaccine is a shot given subcutaneously (under the skin). It is recommended for all children under 13 and for everyone 13 or older who has never had chickenpox. In the United States, two doses are recommended by the CDC. For a routine vaccination, the first dose is administered at 12 to 15 months of age and a second dose at age 4–6 years. However, the second dose can be given as early as 3 months after the first dose. If an individual misses the timing for the routine vaccination, the individual is eligible to receive a catch-up vaccination. For a catch-up vaccination, individuals between 7 and 12 years old should receive a two-dose series 3 months apart (a minimum interval of 4 weeks). For individuals 13–18 years old, the catch-up vaccination should be given 4 to 8 weeks apart (a minimum interval of 4 weeks). The<unk>  did not become widely available in the United States until 1995. In the UK, the vaccine is only recommended in people who are particularly vulnerable to chickenpox. As there is an increased risk of shingles in adults due to possible lack of contact with chickenpox-infected children providing a natural boosting to immunity, and the fact that chickenpox is usually a mild illness, the National Health Service cites concerns about unvaccinated children catching chickenpox as adults when it is more dangerous.
Varicella vaccine
Measles vaccine
Hantavirus vaccine
Typhus vaccine
Polio vaccine
Typhoid vaccine
Ebola vaccine
Mumps vaccine