Epidemiology

Varicella-zoster virus (VZV) is found worldwide and is very contagious.[1]​ Over 90% of unimmunised people become infected, but infection occurs at different ages in different parts of the world; over 80% of people have been infected by the age of 10 years in the US, the UK, and Japan, and by the age of 20 to 30 years in India, Southeast Asia, and the Caribbean.[2]​​[3][4]​​ The virus is more prevalent in temperate climates, and outbreaks are more common in late winter and spring.[5] Estimated hospital admission rates for varicella in developed countries range from 2 to 6 per 100,000 people and appear to be higher in African-American people and non-white Hispanic people.[6][Figure caption and citation for the preceding image starts]: African patient with varicellaImage provided by the CDC and the Public Health Image Library [Citation ends].com.bmj.content.model.Caption@554106b7

Serosurveys in the US before immunisation was introduced have shown that more than 90% of individuals had VZV antibodies in adolescence and nearly 100% had them by adulthood.[7]​ The greatest incidence of varicella is in children 1 to 9 years of age, but in tropical climates, particularly in rural areas with smaller population densities, the disease is often acquired in adulthood.[1][8]​​[9]​​​​​ Immunocompromised patients are at greater risk of complications and mortality. The mortality rate due to varicella is low. In 2012-2016, the annual average age-adjusted mortality rate for varicella was 0.03 per million population, which is a reduction of 94% compared with pre-vaccine period, and a 47% reduction compared with the period 2005-2007.​[10]

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