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Authorities and doctors are warning parents who want to avoid chicken pox vaccines for their children that a new mail-order scheme to share lollipops licked by children infected with the disease as a way to create immunity in their kids is not only unsafe but illegal.

“Can you imagine getting a package in the mail from this complete stranger that you know from Facebook because you joined a group, and say here, drink this purported spit from some other kid?” U.S. Attorney for the Middle District of Tennessee  Jerry Martin told The Associated Press.

News reports from Phoenix’s KPHO-TV and Nashville’s WSMV-TV this week looked into groups forming on social media sites like Facebook that offer ways to get “natural immunity” from chicken pox by deliberately exposing children to the disease.

Concerns about the vaccine range from worries about whether some of the ingredients are harmful to children, to fears that the vaccine itself is ineffective and would only be creating only short-term immunity to the disease.

Facebook groups such as “Find a Pox Party in Your Area” have popped up — offering ways for people to connect and share the virus through infected items, according to the TV news reports.

Doctors warn that the practice is not only impractical, but it’s dangerous.

Isaac Thomsen, a specialist in pediatric infectious diseases at Vanderbilt Children’s Hospital, told the AP that shipping the infected items is “theoretically possible” but “probably not an effective way to transmit it. It typically has to be inhaled.”

But Thomsen also warned that the lollipops could carry other more dangerous viruses, like hepatitis.

It is also federal crime to send diseases, viruses or a contagion through the post office or any mail transport service and carries a sentence between less than a year to 20 years if convicted, according to Martin.

In 1995, the chickenpox vaccine, varicella, was approved for use in the United States. Every state requires  every child be vaccinated before they can enter day care or school.

There are some exceptions that vary state to state, including proof that the child has contracted the virus on his or her own and as parents who refrain from getting their children vaccinated due to religious reasons.

ABC News’ Emily Friedman and The Associated Press contributed to this report.