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25 Years of Chickenpox Vaccine: 91 Million Cases Prevented

WASHINGTON, DC — In the 25 years since the United States first launched its universal vaccinations program to protect children against chickenpox (varicella), the program has seen dramatic results, a data analysis indicates.

Results from 1995 — when universal vaccinations began — through 2019 were presented Thursday at Infectious Disease Week (IDWeek) 2022 Annual Meeting by Mona Marin, MD, a medical epidemiologist at the Centers for Disease Control and Prevention (CDC). Researchers analyzed published data and surveillance data reported to CDC.

Deaths in Under-20 Group All but Eliminated

It’s now rare for children to be hospitalized with chickenpox, and deaths from the infection in people younger than 20 have largely been eliminated. But benefits extend even further.

Immunocompromised people or pregnant women and infants too young to be vaccinated also benefited from the children’s immunizations.

Each year, about 3.8 million cases, 10,500 hospitalizations, and 100 deaths from chickenpox are prevented in the US thanks to the vaccination program, Marin said.

Over 25 years, 91 million cases, 238,000 hospitalizations, and 1,933 – 2,446 deaths have been prevented.

However, chickenpox is still widespread in most of the world.

US First With Universal Program

The disease was thought to be of little consequence, Marin said, until the mid-1950s after the first cases of fatal varicella in immunocompromised children revealed the virus’ lethal potential.

The US was the first country to introduce a universal vaccination program, Marin said. At the time, it was a one-dose vaccine. Within the first 10 years of the one-dose program, chickenpox cases, hospitalization, and death rates declined from 71% to 90% in comparison with previous years. But healthcare leaders wanted to close the remaining gap and target transmission in schools.

“It was a burden the United States considered unacceptable,” Marin said.

The leaders had seen the control of measles and polio and wanted the same for chickenpox.

Two-Dose Vaccines Started in 2007

In 2007, the current two-dose policy was introduced. Administration of the first dose is recommended at age 12–15 months, and the second at age 4–6 years. Vaccination is required before entering kindergarten.

Coverage was high ― at least 90% — the study authors reported; the two-dose program further reduced the number, size, and duration of outbreaks. Over the 25 years, the proportion of outbreaks with fewer than 10 cases increased from 28% to 73%.

By 2019, incidence had dropped by 97%,hospitalizations were down by 94%, and deaths had dropped by 97%.

The biggest decline was seen in those younger than 20, who were born during the vaccination program. That group saw declines of 97% to 99% in cases, hospitalizations, and incidence compared with rates before vaccinations.

Marin says one dose of the vaccine is moderately effective in preventing all varicella (82%) and is highly effective in preventing severe varicella (more than 97%).

“The second dose adds 10% or more improved protection against all varicella,” she said.

But there have been gains beyond medical advances.

Researchers calculated the economic benefit and found a net savings of $23 billion in medical costs (which also factored in lost wages from parents staying home to care for sick children).

Jaw-Dropping Results

Jeanne Marrazzo, MD, director of the Division of Infectious Diseases at the University of Alabama–Birmingham, told Medscape Medical News that “as someone who is not a vaccinologist, the declines in deaths, let alone hospitalizations, were jaw-dropping. I hadn’t really seen a synthesis of the impact of one and two doses.”

She said the declines in zoster among young people were interesting. The big question, she said, is what impact this may have for shingles infections in middle-aged adults over time, since chickenpox and shingles are caused by the same virus.

Marazzo also noted the economic savings calculations.

“It’s such a cheap intervention. It’s one of the best examples of how a simple vaccine can affect a cascade of events that are a result of chronic viral infection,” she said.

There are also messages for the current debates over COVID-19 vaccinations.

“For me, it is further evidence of the profound population-level effect safe vaccines can have,” Marrazzo said.

The authors and Marrazzo report no relevant financial relationships.

Infectious Disease Week (IDWeek) 2022 Annual Meeting: Abstract 801. Presented October 20, 2022.

Marcia Frellick is a freelance journalist based in Chicago. She has previously written for the Chicago Tribune, Science News, and, and was an editor at the Chicago Sun-Times, the Cincinnati Enquirer, and the St. Cloud (Minnesota) Times. Follow her on Twitter at @mfrellick.

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