U.S. Chickenpox Vaccine Program Led to Near Elimination of the Virus

WASHINGTON -- The odds of children becoming infected with chickenpox have decreased since universal vaccination was recommended in the U.S., with deaths also decreasing, researchers said here.

Within 10 years of initiating the vaccine program with one dose of the varicella vaccine in 1995, the incidence of chickenpox cases, hospitalizations, and deaths declined by 71% to 91% compared with the time before the vaccine was available, reported Mona Marin, MD, of the CDC's National Center for Immunization and Respiratory Diseases, during a presentation at IDWeek.

However, because limited transmission was still occurring in school settings, a two-dose schedule was initiated in 2007. By 2019, cases decreased by over 97%, hospitalizations decreased by 94%, and deaths decreased by 97%.

Among individuals under the age of 20, there was an even greater positive impact, with decreases of 99%, 97%, and 99%, respectively, she noted. Even people over 50 years of age saw a 97% reduction in deaths.

During the period studied before introduction of the vaccine (1990-1994), the annual mortality rate from chickenpox was 0.4-0.6 per million population per year.

Over the last 25 years, vaccination resulted in 91 million cases prevented, 238,000 hospitalizations prevented, and 1,933-2,446 deaths prevented.

"For chickenpox to go from an inevitability of childhood to being rarely seen in just one generation is truly remarkable," Marin said. "The significance of the vaccine program -- in lives saved, in sickness and in hospitalizations avoided, and in prevention of disruption to schools and family life -- cannot be overstated."

Children are not the only group to benefit, she added. As more kids were vaccinated, chickenpox transmission decreased significantly in the general population. This shift helped protect the most vulnerable who could not receive the vaccine: immunocompromised individuals, pregnant individuals, and infants too young to be vaccinated, she noted.

"The United States was the first country in the world to implement a universal chickenpox vaccination program. This degree of control of the disease in the United States was unimaginable just 25 years ago, but picture that on a global scale," Marin said. "As science continues to advance, the chickenpox vaccine is a testament to the transformative power of public health."

She estimated that the vaccine program has also saved the American public $23 billion since 1995.

"This [study] is good news," Christian Sandrock, MD, of the University of California Davis in Sacramento, told MedPage Today. "I was a health officer for a while and as a health officer, these are the kinds of data you love to see. This is why we work in these fields."

While there is no federal law mandating vaccination, all 50 states and the District of Columbia mandate that children entering school have at least one vaccination against varicella. In most states, two doses are mandated. Marin said that the acceptance of the two-dose strategy is now on par with acceptance of the two-dose measles, mumps, and rubella vaccine.

Two doses of the vaccine are recommended, the first when children are about 12-18 months old, and the second when they begin to attend kindergarten or elementary school at ages 4-6 years.

Compared with the one-dose varicella vaccine, which was prevalent in 2005-2006, the two-dose vaccine resulted in the following decreases in cases:

• 76% in those under 1 year
• 74% in those 1 to 4 years
• 95% in those 5 to 9 years
• 92% in those 10 to 14 years

Despite the success of the U.S. vaccine program, chickenpox is still widespread in most of the world, Marin noted, urging clinicians to remain vigilant.

Comment