Risk Factors

The varicella-zoster virus is responsible for both chickenpox and herpes zoster, but its method of infection is different in both diseases.

• Both the active varicella and zoster form of the virus can cause chickenpox.
• The shingles virus in its latent (inactive) form is never infectious.

Catching Chickenpox. Most people get chickenpox from exposure to other people with chickenpox. It is most often spread through sneezing, coughing, and breathing. It is so contagious that few nonimmunized people escape this common disease when they are exposed to someone else with the disease.

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People can also catch chickenpox from direct exposure to a shingles rash if they have not been immunized by vaccination or a previous bout of chickenpox. In such cases, transmission happens during the active phase when blisters have erupted but have not formed dry crusts. Herpes zoster spreads only from the rash. A person with shingles cannot transmit the virus by breathing or coughing.

Developing Shingles. Shingles itself can only develop from a reactivation of the varicella-zoster virus in a person who has previously had chickenpox. In other words, shingles itself is never transmitted from one person to another either in the air or through direct exposure to the blisters.

Risk Factors for Chickenpox (Varicella)

Between 75% and 90% of chickenpox cases occur in children under 10 years of age. Before the introduction of the vaccine, about four million cases of chickenpox were reported in the US each year. Since a varicella vaccine became available in the US in 1995, however, the incidence of disease and hospitalizations due to chickenpox are showing a dramatic decrease of over 80% in some states. Experts expect the disease to become a rarity in the US.