Varicella vaccine dramatically reduces morbidity, mortality in children

The chicken pox vaccine has been an unqualified success, dramatically reducing deaths and hospitalization in young people, even among groups that cannot be vaccinated.

In its first 12 years, the single-dose varicella vaccine produced a 97% drop in mortality rate for children and adolescents younger than 20 years, according to a recent study.

With the introduction of the 2-dose vaccine in 2006, researchers speculated that varicella-related deaths in the United States could be eliminated or reduced to extremely low numbers in the future, similar to those seen for measles and polio.

Before the vaccine’s introduction, there were 13 deaths from varicella each year in the United States among children aged 1 to 4 years and 16 deaths in the 5- to 9-year-old age group. For the 6 years from 2002 to 2007, a total of 6 children younger than 9 years had died.

The high degree of immunity in the population has had a particularly beneficial effect on infants.  From 2004 to 2007, no infants died of varicella, even though children younger than 1 year cannot themselves be immunized.

The success is in large part because of the herd immunity created by high vaccination rates in young children.  By 2007, 90% of children aged 19 to 35 months and 76% of those aged 13 to 17 years had been immunized. Of the 77 deaths reported to the Centers for Disease Control and Prevention (CDC) from 1997 to 2007, only 2 occurred among children who had received the 1-dose vaccine, and both were on steroid therapy at the time of death.

Although the 1-dose vaccine is about 85% effective in preventing any occurrence of varicella, it is 97% to 100% effective in preventing severe cases of the disease, resulting in a 65% to 88% decline in hospitalization in all age groups. At the same time, incidence of the disease has dropped 90%.

The 2-dose vaccine recommended since 2006 has an effectiveness of 98.3%, according to a study earlier this year.

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