Chickenpox is one of the most common childhood illnesses. It is a viral infection caused by the Varicella zoster virus and produces a painful, itchy rash with small, fluid-filled blisters.
It occurs most often in early spring and late winter and is highly contagious. Typically, chickenpox occurs in kids between 6 and 10 years of age.
A new study shows that among schoolchildren, two doses of the chickenpox vaccine is more effective than one.
Giving the first dose at age 1 and the second dose at ages 4 to 6 is nearly 100 percent effective in preventing the once common childhood disease, researchers have found.
"A second dose of varicella [chickenpox] vaccine provides school-aged children with better protection against the chickenpox virus, compared to one dose alone or no vaccination," said lead researcher Dana Perella, of the Philadelphia Department of Public Health.
Two doses of the vaccine protected against the moderate to severe chickenpox infections that can lead to complications and hospitalizations, she said.
Before routine chickenpox vaccination began in 1995, virtually all children were infected at some point, sometimes with serious complications. About 11,000 children were hospitalized each year for chickenpox, and 100 died annually from the disease, according to the CDC.
One-dose vaccination greatly reduced incidence of chickenpox, but outbreaks continued to be reported in schools where many kids had been vaccinated. That led the CDC in 2006 to recommend a second vaccine dose.
To evaluate effectiveness of the double- dose regimen, Perella and colleagues collected data on 125 children with chickenpox in Philadelphia and northern Los Angeles and compared them with 408 kids who had not had the disease.
They found that two doses of the vaccine was slightly more than 97 percent effective in protecting kids from chickenpox.
"With improved protection provided by two-dose varicella vaccination compared with one-dose only, continued decreases in the occurrence of chickenpox, including more severe infections and hospitalizations, are expected as more children routinely receive dose two between the ages of 4 and 6 years," Perella said.
For children with weakened immune systems that cannot take the vaccine, having their classmates and playmates protected by the vaccine helps protect them against the viral infection.
School vaccine requirements should include two-dose varicella vaccination, Perella said.
"In addition, 'catch-up' varicella vaccination is also important," she said. This applies to anyone over 6 who haven’t had a second vaccine dose, especially if they could be exposed to chickenpox or shingles - a painful condition in older people caused by reactivation of the chickenpox virus, she said.
Most healthy children who get chickenpox do not have serious complications from the illness. But there are cases when chickenpox has caused hospitalization, serious complications and even death.
A child may be at greater risk for complications if he or she:
· Has a weakened immune system
· Is under 1 year of age
· Suffers from eczema
· Takes a medication called salicylate
· Was born prematurely
The report was published online March 14 and will appear in the April print issue of the journal Pediatrics.
Story sources: Steven Reinberg, http://www.webmd.com/children/news/20160314/two-dose-chickenpox-shot-gets-the-job-done-study-shows