A new study has revealed how cases of chickenpox – the bane of many parents – have continued to decline in the US due to increasing vaccination coverage.
The highly contagious infection, also known as Varicella, has often been a common worry for parents as children are highly susceptible to the contagious disease.
It is caused by the varicella-zoster virus, which also causes the development of shingles in adults.
Before the introduction of the vaccine in 1995, an estimated 4 million cases of chickenpox were recorded every year. The majority of these were children, with approximately 90% of cases occurring before the age of 15.
The airborne disease can be spread easily by sneezing and coughing and, if left untreated, can prove to be life-threatening to the patient.
Prior to the vaccine, the disease was widespread with numerous outbreaks occurring around the country, with schools often the highest area of risk due to the close proximity children share.
At this time, the Centers of Disease Control and Prevention (CDC) estimated 10,600 people were hospitalized every year, with 100-150 fatal cases recorded.
The severity of the disease increases in adulthood, hence, the “pox party” was created – where children were deliberately infected with chickenpox with the belief it would provide immunity against the disease later.
“Pox parties” are now uncommon since the vaccine was introduced. At first, fatal cases of chickenpox did decline, but it was found outbreaks were still occurring even in high vaccination coverage areas.
A second dose of the varicella vaccine was recommended in 2006 and added to routine vaccination programs in response. The first dose is typically given to infants aged 12-15 months of age, followed by a second dose to children aged 4-6 years old.
This latest study – published in the Journal of the Pediatric Infectious Disease Society – saw CDC researchers Jessica Leung and Dr. Rafael Harpaz investigate the current status of chickenpox in light of the vaccination systems implemented 20 years ago.
By drawing on national health care claims data from 1994-2012, they found hospitalizations for chickenpox had declined by 93% since the vaccine was introduced, with the largest decline found among children and adolescents aged 1-19.
Researchers also investigated the effect of the two-dose vaccine and discovered cases of hospitalization reduced by 38% during this period.
In addition, the team discovered the number of outpatient visits had declined. There was also a decline of hospitalizations among infants, for whom the vaccine is not recommended, and adults, who have often not been vaccinated.
Interestingly, this suggests both groups have gained some resistance against the disease through herd immunity – a concept in which the majority members of a community are protected, meaning chances of outbreak are minimized due to the containment of the disease.
“The surrounding population that can be vaccinated are not getting sick, and therefore the data suggest that these infants are also being protected,” Leung explains. “We are seeing that for adults as well.”
The study also found the percentage of outpatient visits for chickenpox in which patients were tested for the disease increased substantially, from 6% in 2003 to 17% in 2012.
The authors conclude that lab testing would become increasingly important in future studies to ensure health care professionals diagnose chickenpox accurately because it can share its symptoms with other conditions. For example, patients diagnosed with rubella also develop an itchy rash that spreads across the body.
MNT previously reported on a 2013 study that stated the vaccine has mostly neutralized chickenpox.