Fewer Chickenpox Cases in American Houses

Chickenpox vaccine with second dose led to decline in infections and deaths

/ Author:  / Reviewed by: Robert Carlson, M.D Beth Bolt, RPh

(RxWiki News) Chickenpox was once a disease that nearly all children caught and some children even died from. Now most children receive the chickenpox vaccine.

A recent study found that the introduction of the vaccine and a second dose of the vaccine has dramatically reduced infection rates.

Deaths and hospitalization have also decreased as a result of the vaccine's use in the US.

Chickenpox is caused by the varicella virus.

The one-dose varicella vaccine was introduced in the US in 1995. A second dose was recommended in 2006.

"Talk to your doctor about the CDC immunization schedule."

The study, led by Stephanie Bialek, MD, MPH, of the Division of Viral Diseases at the US Centers for Disease Control and Prevention, looked at the effectiveness of two doses of the chickenpox vaccine.

The researchers looked at the rates and severity of chickenpox infections between 1995 and 2010 in Antelope Valley, Calif. and West Philadelphia, Penn. They found that the number of chickenpox infections decreased 98 percent from 1995 to 2010.

There were also significant declines from 2006, when the second dose was added, through 2010.

In 2010, three out of every 10,000 people in Antelope Valley, California caught chickenpox, and 1 out of every 10,000 people in West Philadelphia caught chickenpox.

Compared to the rates in 2006, these infection rates represented a 76 percent decrease in chickenpox in Antelope Valley and a 67 percent drop in West Philadelphia.

The decrease in cases from 2006 to 2010 was seen across all age groups.

Across both city populations, 62 percent of those who got chickenpox had received one dose of the vaccine, and 7.5 percent had received both doses of the vaccine.

This difference revealed the greater protection offered by the second dose of the vaccine.

Even though some individuals who had been vaccinated still got chickenpox, their experiences with the disease were milder.

Most (63 to 70 percent) of the vaccinated patients who caught chickenpox had fewer than 50 overall lesions (the red, itchy pockmarks).

The researchers also found that fewer and fewer individuals needed to be hospitalized for chickenpox during the period after the second dose of the vaccine was introduced.

From 2006 to 2010, more than 40 percent fewer people were admitted to the hospital for chickenpox than during 2002 to 2005.

When the 2006-2010 hospital admissions were compared to those from 1995 to 1998, the decline in people admitted for chickenpox was more than 85 percent.

Finally, the researchers found that only about a quarter of the number of outbreaks occurred after 2007 compared to the four previous years.

There were only 12 outbreaks across the US between 2007 and 2010, but there were 47 between 2003 and 2006.

Between 1995 and 1998, there were 236 chickenpox outbreaks across the US.

The researchers found that the drop in infections occurred even among babies too young to be vaccinated and among adults who had not been vaccinated or ever had the disease.

The decrease across all age groups means that the widespread use of the vaccine has resulted in protection for un-vaccinated individuals (like babies) through herd immunity.

Herd immunity is the concept that an entire community, including those who cannot be vaccinated, is protected from a disease because enough people are vaccinated to prevent the disease from traveling through the community.

"The varicella vaccination program in the United States has resulted in dramatic declines in varicella incidence, hospitalizations, and deaths," the researchers wrote.

"Declines in incidence across all ages, including infants who are not eligible for varicella vaccination, and adults, in whom vaccination levels are low, provide evidence of the benefit of high levels of immunity in the population," they wrote.

Thomas Seman, MD,  a pediatrician at North Shore Pediatrics in Danvers, Mass., said he is frequently asked why a chickenpox vaccine is needed.

He said in addition to the possibility in rare cases for hospitalization or death, there are also long-term and short-term ramifications of the disease.

"Short-term ramifications include increased infections of these pox or lesions," he said. "In the last decade there has been a significant rise in community-acquired MRSA infections. Nowadays, in most areas the majority of skin infections are MRSA."

MRSA stands for Methicillin-resistant Staphylococcus aureus, a more dangerous and infectious form of bacteria that is already present on a person's skin. Mithicillin is an antibiotic.

"These infections are hard to fight and have an increased chance of causing scarring as well as significant illnesses," Dr. Seman said. "With the average unvaccinated child having at least 300 pox, this gives MRSA the opportunity to infect the child 300 times."

Significant infection can result, he said, requiring hospitalization, IV antibiotics and sometimes even surgical removal of the infected tissue. "This is rare, but the risk is increasing and are only way of controlling it at this time is to immunize," he said.

The long-term ramifications of chickenpox refer to shingles, which are caused by the same virus (varicella) as chickenpox that can "come back" from the suppressed chickenpox virus in a person's system and cause painful lesions on large areas of the skin.

"These lesions will feel like fire on one skin and can last for months to years," Dr. Seman said. "Although the vaccine itself is a live vaccine, the risk of shingles related to the virus given for immunization is significantly less than a wild type disease."

Dr. Seman pointed out that widespread immunization also offers herd immunity to protect those who have compromised immune systems, are receiving chemotherapy or immunosuppressive medication, are too young to receive the vaccine or are adults who did not have the chickenpox as children.

"This group of people are at greater risk for having serious side effects associated with the infection, which can include meningitis, a viral pneumonitis and overwhelming sepsis [serious infection]," he said. "Unfortunately, as with all vaccines, there is not 100 percent protection, but as the study showed, should someone vaccinated still get chickenpox, their illness is reduced at least five-fold."

The study was published October 7 in the journal Pediatrics. The research was funded by the CDC. The authors declared no conflicts of interest.

Review Date: 
October 7, 2013
Last Updated:
October 27, 2013