While most of the focus has been on the logistics of enforcing Maryland’s latest vaccination deadline for students in grades six through nine, public health officials say that the medical reasons for the requirement imposed by the state legislature have received scant attention.

Contrary to popular belief that chickenpox is a mild illness, Reed and other health officials say, it is impossible for doctors to predict who will suffer serious complications, the risk of which increases with age. The most dreaded includes necrotizing fasciitis, the so-called “flesh-eating bacteria,” which can be fatal.

“Every doctor who has seen a case of this hopes never to see one again,” said physician Deborah Wexler, executive director of the Immunization Action Coalition, a nonprofit Minnesota group that provides informational materials about vaccines to doctors and works closely with the federal Centers for Disease Control and Prevention.

“People who don’t vaccinate their children are putting them at risk, as well as kids who can’t be vaccinated” because they have cancer or other medical problems, Wexler said. “This is about protecting yourself and protecting your community.”

Once accepted without question as a parental responsibility, immunization has lost the urgency that used to propel it, Wexler and others say, in part because mass vaccination has been so successful.

Most parents have never seen or heard of children who went blind from measles, deaf from mumps or suffered overwhelming infection from other childhood diseases such as haemophilus influenza.

Some of the skepticism about the need to vaccinate is attributable to what many health officials say are persistent unsubstantiated myths about childhood vaccines that circulate on the Internet: that the dangers of vaccines outweigh their benefits, that they cause autism and other serious ailments or that they encourage promiscuity.

Much of the controversy has swirled around mercury, which was once used as a preservative for the vaccine against measles, mumps and rubella known as the MMR.

In 19 states, lawmakers have made it easier in recent years for parents to opt out of vaccinations based on a “personal belief exemption” that in some states may be obtained simply by signing a waiver. (In the District, Maryland and Virginia, exemptions are permitted for religious or medical reasons, such as a severe allergy to a vaccine component.)

“The MMR controversy did a lot of damage and made people scared of vaccines,” Wexler said.