child with chicken pox
Close to one-quarter of students at a California elementary school have been directed by school officials to stay home for three weeks due to a small onset of chickenpox cases that began in March.

The chickenpox outbreak at Mariposa School of Global Education in Augora Hills, California is unique because the first case of chickenpox discovered at the school was found in a student who had been fully vaccinated.

Daniel Stepenosky, the superintendent of Las Virgenes Unified School District that includes the Mariposa School, acknowledged to CBS Los Angeles that three students were found to have chickenpox. "A kindergartener, a first-grader, a third-grader. The first case happened around mid-March. The student was immunized, however still contracted chickenpox."

According to local newspaper The Acorn, Stepenosky noted that "(It's) interesting . . . the first of three cases was a student that was fully immunized. . . . He was the vaccinated one."

This student was reported to have contracted the disease back in March. After two more cases were found, the school district took action to keep the unvaccinated students out of school for three weeks.

While individual school policies vary according to state laws, it's typical for school officials to notify parents who do not vaccinate their children when an outbreak of a vaccine-preventable disease occurs. About 400 students attend Mariposa School of Global Education. Around ninety of those students have not been vaccinated for chickenpox, and on May 1st the parents of those students were ordered to keep their children home for 21 days.

"Given that there were three cases, given that they were in three different grades, the health department gave the directive to exclude students who are not immunized," said Stepenosky.

Vaccination rates at the Mariposa School have risen greatly in recent years. In 2015, it was reported that about 40% of the students were current on vaccinations; following changes in state law, that number is up to 80%.

In 2016, the state of California halted the allowance of personal and religious exemptions for vaccinations, and currently, only medical exemptions issued by licensed doctors are allowed.

"There are legitimate medical waivers," Stepenosky said. "For example, a student with a compromised immune system, which could be for any reason, is often because they are fighting cancer."

The chickenpox vaccine has been reported by the Centers for Disease Control and Prevention to be 90% effective if an individual has received two doses.

The CDC also notes that "some people who are vaccinated against chickenpox may still get the disease. However, it is usually milder with fewer blisters and little or no fever."