Amid a national debate on vaccines for children, Michigan health officials implored parents this week to keep children's vaccinations up to date following recent chickenpox outbreaks. The Michigan Department of Health and Human Services said Tuesday that outbreaks have been reported in multiple counties involving mainly unvaccinated children in school settings.

The outbreak had spread to Calhoun, Grand Traverse, Muskegon and Wayne counties even though immunization against chickenpox, as well as other diseases, is required to attend public school in Michigan. But a state law allows parents to waive the requirement.

Government officials across the nation have debated vaccine requirements and school exemptions amid a growing concern that parents who won't vaccinate their children are making the nation sicker. In California, Gov. Jerry Brown recently signed Senate Bill 277, which includes stricter school immunization requirements.

"The science is clear that vaccines dramatically protect children against a number of infectious and dangerous diseases," Brown said in a statement at the time. "While it's true that no medical intervention is without risk, the evidence shows that immunization powerfully benefits and protects the community."

Chickenpox, or varicella, is known for creating an itchy rash that may be preceded or accompanied by fever, tiredness, headache and loss of appetite. It's highly contagious, spreading through coughing and sneezing. In Michigan, some children were hospitalized because of the outbreaks.

“Since the introduction of the chickenpox vaccine 20 years ago, the immunization has greatly reduced the incidence of illnesses, hospitalizations, and deaths related to the disease. Michigan has seen a 97 percent decline in chickenpox in that time,” said Dr. Eden Wells in a news release from the MDHHS. “The best thing you can do to protect your loved ones and community against chickenpox is to make sure your family is immunized.”

An estimated 4 million Americans contracted chickenpox each year before the vaccine became common, Michigan officials added.