Varicella vaccination Effectiveness and Safety
Varicella vaccination Safety and Effectiveness
It is a highly infectious disease caused by Varicella-Zoster Virus (VZV) that transmitted from person to person by close contact, breath of aerosols of vesicular fluid of skin lesions of varicella or herpes zoster (HZ), either it can cause localized, painful vesicular rash commonly which is called shingles, or infected respiratory tract secretions that also might be aerosolized again to cause infection. The incubation period is almost 14–16 days after exposure to rash appear (range: 10–21 days). Infected persons are contagious an estimated 1–2 days before rash onset until all lesions are crusted, typically 4–7 days after rash onset. Usually lifetime immunity achieved by primary infection with VZV.
Health care associated VZV transmission is a well-recognized and can be a life threatening incidence for many patients in hospitals, long term care facilities that can be transmitted from / to patients, health care providers , visitors…etc. it was documented that a single health care provider with unrecognized varicella can result in the exposure of >30 patients and >30 employees. Certain patients without evidence of immunity are at increased risk of acquiring VZV (all at risk ): gestating women, premature newborns born to susceptible mothers, infants born at <28 weeks’ gestation or who weigh ≤1,000 grams regardless of maternal immune situation, and immunocompromised persons of all ages (including persons who are undergoing immunosuppressive treatment, have malignant condition, or are immunodeficient).
VZV vaccination is two doses administered 4-8 weeks apart is recommended vaccine to be administered to children and health care providers (If no evidence of immunity to varicella)
Varicella vaccine among children indicated good performance of 1 dose for prevention of all varicella (80%–85%) and >95% effectiveness for prevention of moderate and severe disease. the second dose among children produces an improved humoral and cellular immune response that correlates with improved protection against disease.Varicella vaccine effectiveness is expected to be lower in adults than in children. Adolescents and adults require 2 doses to achieve seroconversion rates similar to those seen in children after 1 dose. By the 2 doses of varicella vaccine 4 or 8 weeks apart almost 80% reduction in the required number of cases for the exposed persons.
Duration of Immunity
Detectable antibody levels have persisted for at least 5 years in 97% of adolescents and adults who were administered 2 doses of varicella vaccine 4–8 weeks apart, but boosts in antibody levels were observed following exposures to varicella. 25%–31% of adult vaccine recipients who seroconverted lost detectable antibodies 1–11 years after vaccination, vaccine-induced VZV-specific T-cell proliferation was maintained in 94% of adults 1 and 5 years post-vaccination. Disease was mild in vaccinated persons who developed varicella after exposure to VZV, even among vaccinees who did not seroconvert or who lost detectable antibody. Severity of illness and attack rates among vaccinated adults did not increase over time.
The varicella vaccine has an excellent safety profile. The most common adverse events among adolescents and adults were injection-site complaints (24.4% after the first dose and 32.5% after the second dose).Varicella-like rash at the injection site occurred in 3% of vaccine recipients after the first dose and in 1% after the second. Non-localized rash occurred in 5.5% of vaccine recipients after the first dose and in 0.9% after the second Does. In limited cases, some serious adverse events reported among children: pneumonia, hepatitis, HZ (some hospitalized), meningitis with HZ, ataxia, encephalitis, thrombocytopenic purpura (Not all severe reported cases are laboratory confirmed to be caused by vaccine strain VZV).
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