News From Terre Haute, Indiana

December 2, 2012

Vigo chickenpox investigation still under way

Officials may have ruled out bad batch of vaccine

Sue Loughlin
The Tribune-Star

TERRE HAUTE — An investigation into possible causes and contributing factors in Vigo County’s chickenpox outbreak “is still ongoing and will be for months,” according to a spokesman for the Indiana Department of Health.

But state and federal health officials say it doesn’t appear the outbreak was caused by a bad lot, or batch, of vaccine.

Ken Severson, spokesman for the Indiana Department of Health, responded to Tribune-Star questions by email.

As part of the state’s outbreak investigation, IDH “compared all the cases to the lots of vaccine given and have not found any correlation,” Severson stated.

Vaccinated individuals who subsequently developed a mild case of breakthrough disease during the outbreak received multiple lots of chickenpox vaccine over several years, he stated.

Also, those vaccine lots were used in other areas that have not had outbreaks of chickenpox. “Therefore, this [outbreak] does not appear to be related to any particular lot of vaccine,” Severson responded.  

In response to a question, he noted that “Merck is the sole manufacturer of varicella vaccine and has been informed of the ongoing outbreak.”

Tribune-Star efforts to reach a Merck representative on Friday were not successful.

According to Severson, of the  92 cases of chickenpox that have occurred in Vigo County: three were unvaccinated, 26 had one dose of vaccine, 57 had two doses of vaccine, two had a history of the disease and the vaccine history is not known in four cases.

According to Joni Wise, administrator with the Vigo County Health Department, many in the community are asking why so many people optimally immunized developed the disease, although in a milder form. They are asking why  the vaccine didn’t work in so many cases.

Jeanette St. Pierre, of the Centers for Disease Control, said “the varicella-zoster virus is a very stable virus and thus is not likely to have ‘morphed’ into a different strain,” making the vaccine less effective.

She provided answers to questions by email.

St. Pierre further stated, “Although the varicella vaccine has been successful at reducing disease, one dose is 80 to 85 percent effective in preventing disease, so we expect about 15 to 20 percent of vaccinated persons to develop disease if exposed.

“We still don’t have much information on the effectiveness of two doses in field settings, but it is more effective than one dose. However, it is not 100 percent effective, so we would expect to see cases among persons vaccinated with two doses (less than among persons vaccinated with one dose),” she stated in the email.

It appears recent chickenpox outbreaks in both Vigo and Parke counties have prompted some changes for next year.

Next year, Severson stated, students in grades 3 through 5 statewide “will be required to have two doses of varicella vaccine to attend school.”  

Due to relatively recent changes in state vaccination requirements, this year, students in kindergarten, first and second grades had to have two doses of vaccine or a history of the disease, as did students in grades 6-12.

Indiana students in grades 3-5 were not required to have that second dose because the requirements only called for one dose when they started school.

Because of the outbreak in Vigo County, all Vigo County School Corp. students had to receive two vaccinations, demonstrate a history of the disease or face exclusion. The district should be in good shape next year, said Ray Azar, VCSC director of student services.

Because of the outbreak, he anticipates the district will “tighten up” some when it comes to students having all their required vaccinations next year, not just chickenpox.

In the past, “We’ve been very vigilant about making sure kids have met vaccination requirements, but we’ve also been flexible in not excluding them until certain points,” Azar said.

Families have received multiple notices, and in some instances students have been given until spring semester before the district starts excluding, he said.

Deadlines may be bumped up next year, although he didn’t want to get too specific. With this year’s chickenpox outbreak, “I think the community at-large realizes the importance of vaccinations,” Azar said.

IDH was asked if there are “any lessons to be drawn from the [Vigo County] outbreak to prevent it from happening elsewhere.”

The response was that parents and providers should make sure children are appropriately vaccinated. Schools should carefully monitor vaccination records to assure children are compliant with school immunization requirements or have valid medical or religious exemptions.

Severson also was asked to define “investigation” when an outbreak occurs.

“When a case is reported to the state or local health department, public health nurses and epidemiologists gather information about the case to determine how the exposure occurred, how long the case will be contagious, and who has been exposed and is at risk for getting disease.

“Public health officials also determine if anyone at risk for severe disease, such as immune-compromised students or teachers, was exposed and offer appropriate recommendations.

“State and local health officials work together to make recommendations to prevent the continued spread of disease based on the findings of the investigation and Centers for Disease Control & Prevention (CDC) recommendations.”  

Once the investigation is complete and the outbreak is over, a report will be written based on the information available, Severson stated. “It may not be possible to answer all the questions that arise as a result of the outbreak.”  

Sue Loughlin can be reached at (812) 231-4235 or